Remember in toy story 2 when Jessie explains about her previous owner Molly? Well in the scene of monsters inc. when they return the child, she gives Selly a few toys. One of those toys had a hat. A hat that looks like Jessie's from toy story 2. So maybe the girl from monsters inc. is Jessie's owner.

its probably just a little easter egg since it's by the same creator

Pixar is notorious for recycling old models. She had a toy Nemo too. And of course the Pixar ball

I doubt we'll ever find out.

yeah but it was implied that that moment occurred years prior to toy story 2 boy can't be older then 3 why would she have give up jessie I agree with animemy love It's just an eater egg

I think it's just an Easter egg, like animemylove said. And actually, Jessie's previous owner was Emily. Molly is Andy's little sister. I'm pretty sure Emily's hair was a much lighter shade than Boo's. Also Boo's bedroom doesn't look much like Emily's--for example, Boo's walls have pink, striped wallpaper all over them, and Emily's are just painted yellow. That's not to say she couldn't have changed her room or moved to a different house at some point, but still... And there's the fact that in that final scene, you see not only Jessie, but also Nemo and the "Pixar ball"--a series of Easter eggs, nothing more.

Haha not to shoot you down or anything, it was a good theory!

Pixar is known for putting easter eggs in their films, most of the time to announce a new film. Monsters Inc was the movie that came out before Toy Story 2.

 

If you take what the Pixar films seriously then apparently Wall-E can be found in the Incredible's garage over a hundred years before he was designed and he also changed tires at the Grand Prix from Cars implying that Wal-Mart Buy 'N' Large installed devices that allow Wall-E robots to travel between different universes.