I don’t think anybody makes compromises that are unwarranted for but to keep a family intact sometimes you need to. Shes going into a new family obviously their family dynamics are different than what shes used to. They have their own values and rules. The desicion is hers she knows more than any of us about whats going to work in their family and what isn’t, and if she doesn’t she’ll soon learn, compromise its just another way of approaching the situation. I just believe you should be the best you can be, and if people can’t see that then there is something wrong with them and not you.
It just sounds like the FIL has a challenging personality, and it plays out in other situations too not just with her. I don’t feel like this is a unique case for him, thats why I suggested she might have to tolerate him in general. He can stay like this, and you will be the better person in dealing with it fairly and calmly, and if you stay consistent he might even regret this one day.
I do agree with the fact that you need to be good on the communications level with your man though, he shouldn’t be kept in the dark, he knows his family and he knows you he has a comprehensive view better than any of us, he should be helping you accomodate into the family and not be alienating you. Hes your best answer in all of this, and communication is the key, I think you’ll find your answers in him.