This is very stressful, I’m sorry you are having to deal with this.
Sadly I agree that you probably cannot prevent her from getting one, but you may be able to help her take better care of it if she does. She also may just be saying she will get one and not actually go through with it… so hopefully that’s the case.
Sometimes it helps to start small… like encouraging her to give unlimited grass hay, or sharing some educational social media accounts (although that might encourage her more). It can be really hard not to get overly upset when you hear about neglect happening, so if that’s the case it can be best to just remove yourself from the situation (as you did already when you moved seats). We all care deeply about rabbit welfare, and one way to help improve the lives of rabbits is to help educate people on what proper rabbit care looks like. It can be overwhelming to try to address everything all at once, but the two things I think are best to start with are diet (unlimited hay, limited pellets are the most important to start with), and having some exercise time in a bunny-proofed room or run.
You are of course not obligated to do any of that, but if you find out she is in fact getting another rabbit, you might decide to. You could initiate the conversation by saying you were sorry for getting mad, and that you just care a lot about rabbits and want to help her take better care of the next one. If she blows you off then there really isn’t much you can do (aside from reporting to animal control as others have mentioned if you suspect very obvious neglect).
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.