I have a story I've been picking at for a while now that features a human girl who was kidnapped as a child and sold as an exotic pet to an alien species. I was thinking she was kidnapped at 7 and is currently 12, but these can be changed if need be. Her only company for years has been her owners (who think she's non-sapient) and two members of a different alien species that are in the same boat as her. She and her companions have made a pidgin they can communicate in, but it is restricted by physical ability to make the same types of sounds and body movements. As for her owners, neither her nor her companions are capable of making the flute-like sounds they use to communicate and her attempts at whistling at them are met with the same amusement that humans have when a cat makes a sound that seems vaguely wordlike.
My question is this: How would this affect her psychologically? By the time the story takes place, would she even be capable of seeing herself as anything more than an animal? I kind of need her to be able to attempt to prove her sapience to her owners, so if anything needs to be tweaked for this please speak up. Also, how different would it be from "normal" isolation since her companions are both sapient albeit not the same species as her?
If it matters, she has the same kind of freedom that a cat does; that is to say she's yelled at for getting on some of the furniture but not all of it. Her companions, being cold-blooded and partially aquatic, are restricted to a heated terrarium with an artificial pond and ledges to sun on. She can enter it whenever, but her owners only let her leave it when they're sure she's not wet enough to track water through their home. Her owners are not deliberately abusive because alien pets are expensive to treat or replace, but accidents have happened.
I have searched "psychological effects of isolation," "feral children," and "neglected children raised by pets," but nothing I found is what I'm looking for. The former has mostly brought up prison reform articles, and the latter two bring up examples that were isolated much younger than my character. Furthermore, they tend to focus on recovery afterwards, whereas I'm looking for during.