Security deposit issue

[Sylvia HC]

It's kind of a long story and involves not a lot of money but I'd like to hear what others would say to this.

We took in a tenant/roommate (we are owners living with our tenants in a roommate situ) when she had great difficulties. She had unemployment checks coming in but no job. (Finally, she got a job 3 months into the tenancy). When she moved in she (cleverly) wrote into our rental contract on the "deposit" line that she will pay deposit by $20 installments per month until paid off. I know we were stupid to sign it. We just wanted to help that's all. She paid her rents (except one month when she was very late).

End of January she announced to our roommates (not to owners) that she will be leaving after we the owners raised the issue of the deposit installments, not being paid, by email. We were happy that she was wanting to leave as all the roommates expressed concerns with her (she was smoking, drinking etc). She paid another installment of $50 and then nothing (still well behind the $20/mo agreement). As she didn't say anything to us the owners I finally wrote up a 30-day notice to make sure she leaves. In the notice I specified that we require her to give us the full deposit requesting an amendment to the rental agreement (in our agreement it says these can be done by either party with a 30-day notice). She refused saying that if she pays she can't move. Now, she has 2 jobs (a full and a part time) so I don't believe her.
Now the cat issue: I found a cat on the street in the winter and took her in. We were to give her away to a friend but our tenant said that her daughter wanted her. We said OK. We had another cat so we had no choice but to feed them/her. I did not keep receipts as it was a 4-month period. When asked if and when the daughter takes the cat the answer was that when she has her own place that allows cats. But she and her daughter did take the cat for neutering on their expense (after several complaints from all the roommates concerning noise).
When she moved out it turned out she got a place with her daughter. We were not in speaking terms at that time. As she had a bird and a dog already and knowing that it is just an apartment they are moving into we were still not 100% if they take the cat or not. Also, due to a family emergency we were away for 2 weeks and we were not home when she moved out.
I would like to deduct the (approximate) expenses for cat food and littler as there is no other way I could get the money from her or her daughter. (She does not respond to any contact). As far as I am concerned she broke our contract already by not paying the deposit so why not I just deduct my expenses toward her and her daughters cat..? Can I get into trouble with this?
Another thing: she took our key even though our roommates (who she basically forced to help her move) requested her repeatedly to leave the key! :roll: