A therapist could help her. When I started to know my mother wasn't "right" we had no diagnoses, and it led to a terrible amount of resentment, which has left scars on my brother and I to this day. Having a diagnoses will help, and a good therapist will help her to talk through it.

But again, you don't have to over therapise her, if you see what I mean... someone professional, kindly and detached from the situation can help her work through it, but I wouldn't have thought she'd need to be in therapy for years about it.

My son internalised his confusion about me, and when he was a teenager and my own diagnoses came through it was a relief to both of us. Hopefully she'll arrive at a point of compassion soon. It's a hard lesson to learn. Good luck.