hi bones,
I don't know if I'm remembering this right, but I believe in the Divorcing the Parent book the author touches on this, and if I remember right she suggests like hops said, reviving some specific old memories with a few props. After you've got an idea of your mother in your mind and are really focusing on the things she did to you that were abusive, hurtful, or otherwise damaging, you can have a conversation with her (use two chairs, pretending she is in one). You can play both parts if you like, switching from her to you.
By confronting your passed N parent in this way, you can give yourself power and them less power over you...
I think that's the idea anyway.
Something that really touched me in this book was when the author explained a grad student of hers, who needed to do this. He kept trying to think of his parent, and the damage, but no emotions (strong ones anyway) would come...it is not an easy task if the pain is very deep, buried so far beneath those layers of protection. Anyway, she (as his T) was able to help him uncover the pain by asking some specific questions - so you can also do the exercise with your T, if they're qualified. Finally, through her questioning he was able to relive the pain, and I remember he said something like "this hurts like Hell.." He was remembering his Dad beating up on him everyday, and he asked things (pretending his T was his deceased father) like: "Dad, why did you do that to me?" and to Mom: " Mom, why did you let him? " The pain is necessary though, cause if it's not released, it is like a hard rock within us.
hugs,
pb