First off I'm a male so I can't be a sister friend
but I can offer a little advice if you want. In life there are some people that you can only love from a distance(meaning if your around them to much either your blood pressure will shoot pass the roof or you'd kill them neither which is good) Secondly your mother seems to have some deep rooted anger going on,if possible maybe you can get her to open up and talk about it.You may be surprised by some of the things that happened in her life, if all this fails rest knowing you did all that is humanly possible to help your relationship. You'll be some what sad but live life to the fullest never allow anyone to steal your joy even if it's family member.
Disclaimer:All my views are only from the stand point of a male a female may totally disagree w/all or part of the above statements.