I think you have the right idea. I think it's nice that your mom might be open to the idea, and that you guys can talk to each other about the past. Like skeksi, I have the opposite problem. (my therapist would love to get my mom in therapy with me; not happening.)

I do think there's some value in "processing" together this way, and it might help you both to get more resolution if you had someone who could help you guide the process a little more.And I think talking to your individual therapist about this is a really good idea...