So Starfire's powers in TT are powered by her positive emotions and when she's sad she can't get them to work - both are explained in different episodes of the show which I can't name off the top of my head but I know their plots- but like surely anger isn't a positive emotion yet when she's mad she can use her powers? 

I read one theory that it takes time for her to use her powers without the need for a positive emotion to fuel it then I have my own theory that she needs a passionate/motivating emotion, not a positive one so you can be passionate with anger/ motivated by anger but not really with sadness that's why she can be angry and use her powers

Let me know if I'm just unable to find the comic run where this is explained better or something this is just my theory to explain things but, in the words of our Lord and saviour that's just a theory A G̶A̶M̶E̶  DC THEORY

EDIT: TW INTENSE INJURIES

Every relationship had tense times and that's completely normal. Starfire and Robin were currently going through one of these tense times. There had been a few times where Robin hadn't sided with his girlfriend and had missed a couple of dates because of work. Robin argued that she wasn't always right and the safety of the civilians they protected came before a dinner date. Starfire argued that he shouldn't have said anything if he wasn't going to side with her and there were three other people perfectly capable of doing the job whilst they spent time together. They had been going back and forth, making jabs here and there. Even during missions, the fighting wasn't paused. The consequences of which would put everything into perspective.

They were fighting robots because apparently there was a discount on them at the villain store and everyone was using them and had been pushed back a few paces. This wouldn't be all too worrying for four of the heroes but Robin, unlike his counterparts, couldn't fly so they needed to move forward before someone had to carry him around for the entire fight. "Keep your robots on your side! I have enough to deal with," Robin shouted to Starfire. He'd only barely dodged the hunk of torn apart metal flying towards his head. Surprisingly, he didn't fancy a concussion. Or decapitation.

"Oh poor you! Hey everyone, fight around Robin!" Starfire snapped. 

"No need to get pissy about it," Robin snapped back. 

"I'm being pissy? When I figure out what that means you're so done for," she argued. She stormed over to him and their teammates decided that the battle was too loud for them to hear the rest of the argument. They didn't want to get in either party's bad books. 

"You always get mad at me for no reason! We have jobs and sometimes that means that we can't do coupley things, you know that," Robin reminded her. She rolled her eyes and punched a robot coming up on their right. 

"I do know that but you're such a control freak! We have other teammates. Friends Raven, Beast Boy, and Cyborg are able to deal with matters whilst we go on dates," she pointed out.

"Sometimes I'm needed or I'm closer to the problem. Would you rather me just let loads of people get hurt? Why don't I just join the villains whilst I'm at it so I can give you more of my time?" Granted that was very dramatic of him and if he hadn't been so worked up already from losing their upper hand he wouldn't have said that. Yet he was also a teenager so of course, he thought it was best to take it too far. Starfire, also being a teenager who was worked up from the battle, took it much further. "I'm starting to think you don't love me. A real boyfriend would spend his time with me and a real boyfriend would say he loves me!" To all of you who are out of the loop, Robin had explained when they began dating that due to past experiences he couldn't say I love you. He said that he did care for her and when she asked do you love me he said yes. It was just extremely difficult for him to say I love you without thinking of all the other people he said that to only to be betrayed or to lose them. He couldn't take that and Starfire had accepted that. That's why right now, she'd taken it too far. She stared at him for a few moments as he looked away in shame. This wasn't what she wanted. They'd taken this so far and now they didn't quite know how to get back to what they'd been before. She stepped closer to him, hesitantly reaching out. "Robin, I didn't-" Suddenly his head snapped up and he yelled, 

"Look out!" 

It went in slow motion. Robin rushed forward and pushed Starfire out of the way as a beam of red light shot towards them. The red beam hit him in the stomach, instantly burning through the material of his suit and cooking his skin. He'd been hit with such force that he'd been thrown off the cliff edge. His brain had knocked him out to spare him of the pain but that just meant when he hit the water below, he sank beneath the waves. Starfire was in shock for the most part. Her whole world went silent as she stared at the spot he'd been but moments ago. He wasn't there. The fight was muffled. Someone was shouting but she couldn't make out what they were saying. She ran over to the cliff edge but she couldn't see the bright colours of her leader's suit. All she could see was the water. She didn't know what to do. There was that shouting again but she couldn't hear it all the same. Robin needed her and she wasn't going to leave him. She took a few steps back before running and jumping over the edge, diving into the water. She opened her eyes and saw a human-like figure sinking whilst being tossed around by the current. Starfire wasn't the strongest of swimmers but she was determined to get him out. He didn't deserve this. The ocean was working against her, pulling Robin to the bottom whilst pushing Starfire to the top. They were a few feet apart now but she was being zapped of strength. Her body was screaming at her to go up for air but her heart was screaming even louder to save him. She'd never forgive herself if she didn't. Her arms were getting tired and her reflexes were trying to get her to breathe though that would only fill her up with salty water. Holding her breath got harder and harder but now Robin was just within reach. She stretched her hand towards his cape and grabbed it tightly, pulling him close. His eyes were closed and his mouth slightly ajar. She had to get him out but now she was being dragged to the bottom. With the added weight of Robin and how tired she was from getting down there, there was no energy left. She thought it was over.

After what felt like an eternity, there was splash above them before a giant killer whale was seen heading straight towards them. Starfire would've winced had she not noticed the shades of green, not the iconic white and black colourings. Beast Boy must've seen what went down. He swam down so Starfire could grab onto his fin and he could pull them to the surface. Starfire gulped down air as soon as she could, coughing up some of the water she'd accidentally swallowed. She repositioned herself on his back and pulled up Robin out of the water. He whined weakly as she kept him close to keep him warm. He was shaking like mad but he wasn't conscious either. "Get us to land quickly!" Starfire ordered, keeping a tight grip of the fin as they rode through the waves.

"Is he breathing?" Beast Boy asked worriedly. Robin's chest was rising and falling shallowly but at least he was breathing.

"Yes but he needs help!" she shouted back over the roar of the water. "C'mon Robin, please be alright," she whispered. Her eyes were tearing up. She couldn't bear things without him. Sure they were going through tough times but couples did. When they got over the argument, Robin would go back to his usual self and be romantic in his own way. She loved his small actions that let her know he loved her. The little post-it notes, how he'd clean her room when she hadn't found the time and he always knew how to calm her down when she felt anxious. "Please, you just have to be alright."

The monotone beep was the only thing Starfire could rely on as she held her boyfriend's limp hand tightly. After the mission, they'd gotten Robin back as fast as they could and the first thing they did was put him in an induced coma so they could treat him. He'd been in the coma for a while now but today was the day he was supposed to be waking up. Cyborg informed the worried alien that he may take longer to wake up thanks to his injuries. She knew the list of injuries off by heart and every single one of them made her feel awful. His burn was bad as the ocean water had caused a nasty infection which had only just begun to clear up and the force of the blow had fractured his bottom ribs. He had bad bruising along his back from hitting the water too so when he woke up he was going to be in a world of pain. Luckily, his head hadn't been too badly damaged and had gotten by with severe bruising. There was some water in his lungs which they had to get out but that problem had been mostly solved right away since, despite it feeling like forever, the pair had only been underwater for a minute or so. Starfire had hardly left his side. She watched over him during the day and slept where she sat at night. It wasn't like she slept much though. He worried her, to say the least. It only took his heart skipping one beat to get her sat up straight and checking every single piece of medical equipment. Sometimes she'd talk to her unconscious boyfriend though most of the time she remained silent, biting at her nails. She couldn't believe it. The last thing he heard from her was a jab at something he was incredibly insecure about. All the times where he'd say it was okay if she didn't want him anymore because of his issues. Those replayed in her mind a lot. She was just so mad in the moment and she prayed he knew she didn't mean it. They both said things they regretted so he probably would get it. She pleaded that he got it.

Midnight rolled around and that's when, like the typical night owl he was, Robin began to stir. Starfire had been just about to go to sleep when she felt Robin's hand tense up. She immediately looked up to him and saw his jaw tense too. He was waking up alright but he was waking up unhappily. His voice was crackly as he let out a quiet whimper as his body let him know he was really hurt. Starfire moved so she could pet his hair as he returned to the land of the living. "Shh Robin, I'm right here." He let out a hiss of pain before finally cracking open his eyes. He glanced around until he found Starfire's face, immediately relaxing when he saw her. He smiled weakly and squeezed her hand to let her know he could hear her. "You got hurt really badly but friend Cyborg promises you'll be okay. It may take some time to heal." He nodded, wincing at the action. He was not looking forward to this. Recovery was the worst. "I'm sorry."

"What for?" he asked. His voice was hoarse but hers would be too if she hadn't drunk water in ages. 

"For saying a real boyfriend would say he loves me." Robin glanced away shamefully as he had done when they were fighting. Before he saved her. "You trusted me with that and I shouldn't have said anything and you can still be mad at me and-"

"Starfire?" 

"Robin?"

"Stop talking," he replied with a small smile. She smiled back and kissed him on the forehead. "I wasn't fair on you. You just became a hero but I've been doing this gig since nine." He took a deep breath between each couple of words but he was determined to get his point across. "I get that I can't be a teenager sometimes but maybe I get it too much."

"I don't understand."

"I'm too ready to give up civilian things for hero stuff. My training says if there's danger, you go stop it but it's not just me and Bats anymore. I have all of you," he continued. "I guess I'm still learning that."

"Does that mean we can have more dates? Outside of hero stuff?" 

"When existing doesn't hurt, yeah," he answered. Starfire grinned, already planning all the places they could go in her head. "Can we try again?"

"I'd like that." He didn't stay awake that much longer, having exerted himself too much. Typical really. Starfire still stayed with him though she now didn't have the weight in her stomach. They were going to try again and maybe when they go through a tense time again it won't take one of them potentially dying to resolve the issues.