You seem to have decided already that you are such a horrible person the whole family won't like you and your T seems to be countering this point. I don't think she doesn't get it, I think she just doesn't agree with your thinking. It's wonderful that both families are trying to come together and if you can try it I think it will be ok, either way it's great material to work on in T. Your son is making you an important part in his life. Go with that if you can.