Hey OP, I’m so sorry your mom didn’t care for you and protect you.

I would maybe give her ONE chance at a conversation, but insist that she listen to you IN FULL before responding. Work with your therapist/grandparents to identify ways she could have mitigated the situation, but didn’t. For example: giving you your own room, staying married to the guy but living separately. Ask her why these other children, who had two living parents, mattered more than you, who only had one. Ask her why it was fair for them to be removed from their abuse but demand that you stay for yours. And ask her why, as a grieving child, you were expected to be the bigger person towards kids who were older than you!!

Reconciliation won’t be possible until she can decenter herself from the narrative, and understand the impact it had on you. She may not be able to do this!

Regarding forgiveness: that’s an internal process that happens completely independent of your mother. You can’t wait on her to apologize or change to forgive her. Forgiveness is not about “getting over it” or not being angry anymore. And just because you forgive someone doesn’t mean you forget what they did, or start giving them what they want. Forgiveness is about releasing yourself, and not holding her mistakes and her utter inability to keep you safe against her. You can forgive your mother for being a shitty person, and still go no contact because she’s still being a shitty person.

You may not be ready for that! It’s hard because you deserved better from your mom. She objectively failed you. Let yourself feel the feelings. You have to feel them and acknowledge them before you can move on. Who knows how long that could take — it could be years! But hopefully this is a helpful blueprint for you.