I've had a parent who has always been a negative person. My mother has always had mental issues, and I've done my best to deal with them. Yeah, I know about always blaming the parents, but everyone dealt with her mental problems by never confronting her. If someone did, her goal was to destroy them emotionally and socially. People that didn't know her just added to the overall problem. I walled away several times for my health and mental health and haven't seen her in months. Now she's got a few months to live. Is it normal not to feel bad because I don't want to see her?

everyone says that the mentally ill person suffers the most, but i, for one, do not believe that. i think that the family of a mentally ill person are the ones who suffer the most.
therefore, i am on you side. don't visit her if you don't want to.
I would suggest going if only to get some form of closure from the whole thing and maybe get some things off your chest. It's amazing what changes faceing the end of ones life brings about in people. She may have a different way of dealing with things or seeing things and even if she doesn't, you should have the opportunity to face what you both went through and try to resolve some of the emotions you may both feel before it's too late.
You came to terms with this to survive. Be at peace with your decision.