I think that boarding Tia is a good part of training her to be with you. You may run into times when she will need to be boarded...I don't think that visiting family should be one of those times, but if they are going to be stubborn....I'd try to find a good kennel, better yet, a home environment for her. That is what my friend has. She takes in dogs at her home. She is a service dog trainer so she could board Tia and train her at the same time!

Maybe you can find someone like her...what about YOUR trainer taking her?