This is very important to realise.
OP, you were obviously very very seriously abused growing up.
I cannot see any advantage to you or your children in being involved.
Your absolute 100% priority is yourself.
To keep yourself as well as possible so that you can be the best mother you can be so that this does not continue into the next generation.
Forcing yourself to be in the presence of someone who terrorised you growing up 80% of the time is not in your best interests.
Mental health is a fragile thing.
You have suffered terribly and now you are trying to force yourself to heal and forgive her.
Nope.
You do not owe her forgiveness, nor contact with you or your children.
Your children deserve a happy well mum, and your best chance of that is to never see this woman again.
Get some counselling for yourself.
Perhaps in the future you may revisit your decision, who knows.
But from what you have described, very very serious child abuse, there is no way I would have her near my children.
Stop pushing yourself to forgive.
There is no deadline.
You can explore the best type of healing for you and what that might look like, but you do not owe her a part of your life.
You do owe your children that you be well and look after yourself.