Hi, I'd like to help you with your question.
It sounds like your mother has not been able to cope with what happened to her as a child and instead of dealing with it, she has transferred her feelings to you. She is also using you as a shield against her father so she can safely (at least in her mind) express her feelings that she cannot say to him face to face.
Although it is difficult to do, you can limit how much you get involved in your mother's issues. Start limiting your contact with her. If she calls you, talk with her. But as soon as she mentions anything about her problems and tries to draw you in, stop the conversation. You can either redirect it, or you can say goodbye and hang up. This is tough to do at first because most adult children feel terribly guilty and upset about what they are doing and feel like they are rejecting their parent. A child's instinct is to always try to love their parents, especially their mother. But loving someone does not mean having to accept abuse. And that love does not give the parent free rein to do what they want, including hurting their child.
If you see her in person, then the same rule applies. Try to keep the conversation about other things. If she ventures into her problems or otherwise tries to use you, let her know you will talk with her again another time then leave.
After a while, she will begin to understand that you will no longer tolerate her behavior. It may or may not change her. She most likely will keep trying to stay on the same pattern with you. It is what works for her and she probably does not know how to change it, especially if she lacks insight. But as an adult, she needs to be responsible for how she is acting instead of using you to cope.
What would help you a lot is talking with a therapist. When you have been abused, it is hard to tell what is normal and what is not. A therapist can help you find the normal so you know when you are being used/abused and can better protect yourself. You can talk with your doctor about a referral or search on line at http://therapists.psychologytoday.com/rms/.
There are also numerous resources to help you at home. Here are some to get you started:
Adult Children of Abusive Parents: A Healing Program for Those Who Have Been Physically, Sexually, or Emotionally Abused by Steven Farmer
Toxic Parents: Overcoming Their Hurtful Legacy and Reclaiming Your Life by Susan Forward and Craig Buck
An Adult Child's Guide to What's 'Normal' by John C. Friel Ph.D. and Linda D. Friel M.A.
You can find these on Amazon.com or your local library may have them for you.
I hope this has helped you,