trans | Therapist wants to meet with a very resistant parent...what to do?

It's not legally necessary at all for my mother to agree to me wanting to transition, but we used to be really close for a really long time, so what she thinks means a LOT to me. So my therapist suggested doing a joint session and bringing her in...I'm really nervous because when I suggested this to my mother, she went on at me that her 'dream' about me was that I would learn to be happy with 'myself' instead of changing.

For one that really hurt, because I don't see my physical body as 'myself' and never have... and for another, the entire reason I am seeing my therapist is to change. I tried making analogies to other 'acceptable' ways people change their bodies, some common things a lot of people do like gaining/losing weight, getting in shape, etc... but it just went over her head. She also insists that she is right, I am delusional, and she doesn't want my therapist to argue with her.

I'm really worried this will make it worse instead of better to do this session. I just don't want to be rejected by the only parent I ever actually felt close to. I'm not a very social person so I mostly just have family to turn to when things are bad, and my mother and I have been through a lot...I just never mentioned this because I was afraid. I finally mentioned it about a year ago, and she's gotten increasingly distant since. I don't want to lose my mother's moral support just for trying to make myself happy.

Has anyone been through similar and/or have any advice for me? Is there a way to make this okay?