I know, I know, ya'll are sick of the theories, well I like 'em so SHUT YOUR TRAP!!! Jk, I'm sorry...

Anyway, here is the theory from the internet:

There is rumor that Andy's mom from the Toy Story trilogy is Emily, the girl that abandoned Jessie. This works very wel since Emily and the mom both have blonde hair. And, Andy has a hat that looked exactly like Emily's. Could have Andy's mom passed down the hat to Andy when she grew older?