I know what you mean about needing a resolution. I never had that with my SM before she died so I'm having to deal with it (2 and 1/2 years and I'm not properly over it :P )
I suggest you make a list of what you want to know. Be brutal if neccesary, you have the right to all the answers from her. Arrange to meet somewhere she can't just storm off easily, or bribe her, since she seems to think she's entitled to see your children you can use that. She's not entitled to any consideration of her feelings, since she appears to have none for you. So don't feel guilty about being underhanded or cruel. Ask the same question over and over until you're satisfied you've got the best answer from her - pretend you're a radio 4 presenter getting an answer from a reluctant politician
Oh, and don't let her get away with blaming her past. She made her own bad decisions, not her own mother, stepmother or other person. I'm sure they made enough bad decisions of their own but that isn't the point.
Once you have an understanding of what her reasons are, you can start to move past it. Forgivness doesn't mean you think she was right, it just means you can get a handle on it and let go of your poisonous negative feelings and that nagging feeling of unanswered questions.
This is what I did to my own mother. She walked out when I was 6 and when I was 15 or so I needed the answers to hard questions. I reduced her to a blubbering wreck before I was finished. I'm still proud of myself that I had the strength to do that! Now I know what happened with my parents I can look at them as weak and stupid and to be pitied rather than heartless and cruel and to be feared or hated. They can't hurt me any more.
On her reason for having a child, I don't know what it is with people thinking they can get the man/woman they're living with to stay by using the kids. That's what my Father did (He tried to keep my mother by telling her she'd lose the kids if she left. She left anyway....) I know at least three women who've had kids to try and save their relationship. It never bloody works and they screw up a new life in the process.
Sorry, one of my bugbears took over there...