You could always try babysitting for a few days and see if stepdad loves her? Otherwise, leave it up to mom. Usually we know when our significant other will bend or not. I know my children back away, or it gets worse. Right now we have the five puppies I want to keep. I just tell them to wait and see. When it is time to get rid of them we may be tired of having 7 dogs in the house, otherwise, he already admits he can't pick which ONE we should get rid of. I guess I am not going to be a breeder.
Good luck with libby.