General Etiquette - FMIL raising hell over wedding shower-does she get to help plan it?

My maid of honor, who is also my sister, is planning my bridal shower with my mom, aunts and grandma. (I'm only having 1 shower by the way-I don't really go in for big events like this, but gave in because it means a lot to my mom). FMIL called to ask if she could help plan the shower and my mother told her no, that our side of the family would handle it and all she and her daughters had to do was show up. FMIL had a fit at this and is very upset. There is bad blood between us because on the first day we met, she told me I was not good enough for her son. I told my mom and sistar about this and they were horribly upset. I have never heard of a fMIL helping to plan a shower-in my family and in all the other families I know and the ones I have been too, the shower planning and duties were handled by only the bride's family. As far as I am concerned, FMIL is lucky to be invited after how awful she was to me. FMIL is also mad because I did not invite her or her daughters to my bridesmaid luncheon and that my mom was there. But her daughters are not my bridesmaids, I am not close to them and my mom was there cause the luncheon was held at my parents house.

I don't know about proper etiquette, but you're allowed to say no...on both accounts. It's obviously a big deal to her and I would try not to be mean about it. Be firm but kind, that way you can say you did nothing to instigate a fight, you kept your nose clean and she's the one with mud on her face if it goes that way. I think she has a strange misconception of bridesmaids too, going on what you said. I think you can tell her this time she's just out to lunch. The same principle goes as before, keep your nose clean, then it's not you in the wrong at all, no matter the subject or who thinks what. That said. She doesn't get to plan (or come to the luncheon). Period.