Hi Celina, I'm just getting caught up here...
I'm so sorry you're dealing with all of this.
I hate to say it, but I know what it's like to have a family member turn on you like that. I had an uncle that did something like that to my parents when I was in college, and with the exception of a few words following my grandfather's death, I haven't spoken with him at all. I think the same is true of all of my immediate family.
I think your conclusions and the advice that most of the people are right. You need to cut her out of your life. That sort of unpredictability and negativity just aren't worth it.
And suggest that she seek counseling. Do it in a way that doesn't make her feel like she was wrong to be protective of your daughter, but just that her immediate assumption that there was a situation of abuse, and her disinclination to discuss it with you like an adult, makes you think that there might be some things in her life that need to be dealt with and a professional could help.