I can't offer any constructive advice, unfortunately, but I can sympathize with you - I've recently redefined my views on my mother (and stepfather) as well, and it's very disconcerting. Almost like having one (or both) of your feet being kicked out from under you.
Best I can say, is to remember all the good things she taught you, all the strengths she has imparted upon you, and realize that the view you had of her all these years was not her deceiving you, but rather seeing her as you needed to in order to grow properly.
You've now entered a new stage of observation; you've reached a point where you can handle the truth, and thus you saw it... And you'll find some way to learn from it.
At least.. That's how I suggest you look at it.
Don't let this new perspective take away any of the faith you have had in her over the years. She raised you better than she herself was raised. Kudos to her.