I was in a similar situation. I was the MOH to my fiance's brother's wedding 2 years ago. I actually "quit" because of how stressed out I was with everything. They had endless parties/ events for them, in which we were both required to attend/ bring gifts and/or money too. We both had just graduated from school, weren't working at the best jobs, and were barely making ends meet. After a debacle of a day going bridesmaid dress shopping, and having Erin tell me that because I was MOH, I could wear whatever colour I wanted, she turned around, lied and said she never said that, and made a big deal about me trying to take over their wedding. I don't lie, I'm far too much of an honest person, and I wouldn't have lied about that, so when his brother called me to ask me why I was being so rude, and why couldn't I get it through my head that this was about them, not about me, I flipped out. I called her, and told her I couldn't do this anymore. I was tired of being made to feel horrible, and that this wedding had become bigger than life, and that I wasn't into it anymore and I quit. Of course, then I got guilted back into doing it, but both my and my fiance hated every second of it, and could not wait for their "big happy day" to end. It put a serious dent into our relationship with them, that we never got over. It ended up being a beautiful day, and we had an amazing time, and forgot all about our issues, for that one day. I think you need to stand up for yourself and let her know how you feel about the situation. But be prepared to continue moving forward, and celebrate their wedding with them. Sometimes, you just have to be the bigger person, and realize that sometimes people act completely irrational in the moment, but they see their fault later on. We can't control other peoples actions, only our own.