I think we also need to know more about how your relationship is at the moment - meaning are you in contact with her or are you estranged? The other posters made a good point, that it might not be possible to have a relationship with a dysfunctional parent. In that case you woud need to decide whether or not to continue or sever contact.

If you do want contact - it might be helpful if you look at your mother just a woman and not a mother. Chances are she also may have been abused when she was a child or she might be mentally ill herself - this changes your perspective and you'll then be able to see her as a 'wounded woman' who needs help. When you view her from this point of view, simply as a human being - you might feel less intimidated by the whole concept.