If your dad is giving her good care and attention and she gets to go inside his home, I would let her stay there. I'm sure you know better where she is happier, but I just feel that an outside only life for a dog isn't good at all. They need to feel like part of the family. I'm sure you spent lots of time with her when she was at your mom's and I know you're a WONDERFUL doggy mom. I just think since your dad is so attached to her and she gets to be inside over there, she might be doing better. Only you know for sure. Does she seem happy when you visit her?