Euthanasia Prevention

My question involves criminal law for the state of: Washington

This situation is a little complicated and this might not be the proper forum. My friend has a dog that technically belongs to his soon-to-be ex girlfriend. This dog is one of two suspected to have attacked and killed one of the families cats. The girlfriend wants to euthanize the dog, while my friend wants to keep it. Is there any legal way for him to "save" the dog from euthanasia?

If the girlfriend is willing, she can sign over the dog to him and then he will be responsible for anything the dog does in the future.

If that's not an option, he can try refusing to let her have the dog. That might not work if she has ownership papers.

If worst comes to worse he can take her to court and seek an injunction against her to prevent the death of the dog and seek possession at the same time.