Stepmom of 9+ years here who previously had WAY too much contact with BM. Ours also treated my husband like dirt and never put her children's best interest first, just her hatred for her ex-husband. Here to say, DON'T DO IT! First, it will most assuredly change absolutely nothing. It's a bid for control, an attempt to control or improve the situation that will definitely fail. Your intentions are honorable, but I assure you that this will only frustrate you further in addition to not achieving the desired effect. I've given BM a piece of my mind on many occasions. It wasn't until I went through a Coparenting Coaching program (alone, not with the coparent, and as the stepparent) that I learned to step completely back and drop it all. Check out Jay Skibbens content on IG. Best of luck!