Is she microchipped ? i.e. Can you prove she is legally yours ?

By outside cat, do you mean Katr is an inside/outside cat right ? You do let her inside ?

Just one thing to consider, who do you think Katr would be better off living with ?

I ask as you said that Katr mother cat was very very mean to her and wouldn't let her eat in peace etc.

If you want her back I would go to the police but you'll need proof of ownership.

Good Luck