Name: Thornfang

This name I've seen quite a few times... consider changing it. 

Age: 26 moons

Young kitty...

Gender: She-cat

Oh god, I would have never known! Normally, a name like Thornfang would be for a male XD Consider changing that...but it's creative of you!

Sexuality: Straight

Clan: RiverClan

Rank: Warrior/Queen

A QUEEEEEEEEEEN :D

Personality: Stubborn, loyal, not very trusting, puts her Clan first, sometimes kind, isn't afraid to claw a mouse-brained cat.

Good personality.

Appearance: Brown tabby she-cat with darker brown stripes, a lighter brown underbelly, and green eyes

OOH, YOU USED BROWN TABBY! YAAAAY :D

Backstory: Was raised in RiverClan as a kit and abused by her mother. Her father died protecting her mother in a battle, so she never got to meet him. Whenever Thornkit/paw needed cheering up, she went to Ashkit/paw. He was very kind, even with his jaw being crooked (like Crookedbae). Her mother eventually ran away due to the stress her clanmates put her through and got run over by a monster. Thornfang and Ashfang, now warriors, became mates. They had two litters of kits.

Whoa. This is a good backstory, but it needs a little more detail. What stress did her Clanmates put Thornfang's mother under? Did Ashkit/paw/fang feel pity towards Thornkit/paw/fang? Plus, the mother-and-father-dying-before-kit-reaches-warriorhood is a bit overused. 

Mate: Ashfang

Yey c: But, I don't think Clan leaders give cats the same suffix in the same Clan.

Kits:

First Litter; Cinderspark, Lionclaw, and Oakpath

Second Litter; Mudpool, Rainfang, Shadestep, and Stoneleaf

Woo! A lot of -fang suffixes in this family.

Family Members:

Mother; Hazeflower (deceased)

Father; Stormystep

These are beautiful names!

Overall Rating: 7.5/10

Your personality is outstanding, your names of her family members are rather creative(other than the repetitious use of the -fang suffix), and I admired the little kithood crush that eventually grew into a full-blown relationship. Change what I suggested above, and you'll avoid falling into a thorn bush that scratches you like fangs ;3

~Stormy