(((((Almeda24Fan)))))
Your Mom's story sounds like it was very painful for her and also very painful to listen to.
I don't like secrets. I don't like parents asking their children to keep secrets. It bothers me. She feels shame about being abused and that is very sad, but I worry that it will become your secret. That's a heavy burden.
After my mother died I found out she had had an affair while we were growing up. I also found out that my father suspected his brother of being my brother's father. Who knows what the truth is? The bottom line for me was that my feelings about my relationship with my mother didn't change because of this new information. It explained some things for sure, about her seeming absence from my life at times. And, other memories and therapy have changed my feelings but not the single piece of information.
Anyway, take gentle care. Best of luck with the session. I am glad T will help you sort this out.