Will therapy always change people for the better?

Hi, I’m asking on behalf of my mother. My sister and I have always had a bad relationship with my mother. She’s incredibly unaccepting and unsupportive of us. She’s distant, and at worst shes outright passive aggressive, and when we stand up for ourselves she reflects it back on us and tells us how unaccepting WE are. For further context, I’m gay, and My mom is very upset about this. This entire situation boiled over 10 years after I came out and started presenting more masculine and have a girlfriend. I’m not going to fully get into it, but it was explosive. A lot of temper tantrums from my mom because shes upset I’m gay and not feminine anymore, she also called me unattractive, and said nobody would care about me because i look like this . I’m in no contact with my mother because she has never apologized for anything she has ever said to us, including this. My entire family is essentially on my side, my father is supportive of me and so is my sister. They managed to get her into therapy because her incapability to accept change and my gayness is actually tearing this family apart.

My concern is, she’s 53. She has been this way my entire life, she even had an incredibly hard time when I went vegetarian as a teenager. She gets so upset when things don’t go exactly her way. She can’t seem to handle me or my sister acting outside of a box she imagined for us. I’m wondering if it’s even worth it to hold on hope because she’s in therapy. I’m also worried that her therapist will tell her all of these wrong things about me, for context, my mom said that her therapist told her I could be dressing masculinely because I hate myself, and my mother wrote me this huge letter begging me to dress femininely again. I can only hope that her therapist first got a warped view of me, My mom sent me that huge letter after 1 month of therapy. I was wondering if anybody had any information regarding this.