Maybe you could explain how you see the situation? Like how her tearing up affects you and that it makes you feel guilty. She may realize that you telling the story isn't meant to share the pain but rather to give clarity on the subject. But she could be right and maybe things do in fact relate to your childhood and it would be worthwhile to get into. If youre open about how her reaction makes you feel maybe you'll find some common ground to work from. Best of luck! I wouldn't let go of a good therapist if I was in this situation but personally I would prefer my T to tear up than not show any emotion at all.