No pet policies at privately owned apartments?

I have a good friend who is going thought a tough time. He has been going to a psychologist for the pass 4 months now for some issues(would prefer not putting them down). About two months in to his sessions he was giving a dog. Very quickly he has been recovering more from his issues, sadly he leaves in an no pet apartment. Landloard quickly discovered his dog and is now telling him to get rid of this dog. Is there anything Law wise that could be used to help him keep his dog, maybe some kind of medical referral? I'm very affrad if he loses his dog he would do something very drastic or fall in to a deep depression.