Sue, I'm so glad you have your sister to talk to about your feelings and I think it's very insightful that you were able to identify your mothers feelings of losing herself in her family responsibilities. I think a lot of women gave up their dreams and that had to cause some resentment.
It's a different time we live in now...*grin. And women get to "do it all" and men have to help them do it. (that's a mixed blessing...definately a change!)
You are of course doing the right thing by talking about it!