Random noter...If it’s not too personal to ask, who’s paying for the wedding? I’ve observed that whoever is holding the pocketbook generally feels entitled to make all the decisions. My husband and I paid for our own wedding and while we had to keep things simple, it was nice to not have to answer to anyone.
If she’s financially involved then you really only have two options—stand up for yourself and tell her to butt out, and hope for the best, or throw in the towel and let her do all the planning without you. But giving in every time she throws a fit definitely won’t make her stop, it will just make her throw more fits.