MIL Problems... please help

So I’ve been having some troubles with my future mother in law. My fiancé and I are getting married in May and no doubt the wedding planning has been stressful (another story for another day). He and I work things out great and always make sure we have great communication. For the past month, however, things have been a little extra stressful. I’ll go straight into it: 1. We wanted a small wedding, my MIL didn’t. We are now having a wedding with 150 people and my fiancé and I each have 9 people in our party. She threw a weeping fit until we agreed. 2. I didn’t want flowers for centerpieces. Me, personally, I don’t find the reasoning behind spending 2k on flowers that are just going to be thrown out. We are having orchids in water for centerpieces and now I not only need to buy the flowers but also the vase, the floating candles, and the rocks for underneath. 3. My sister is my matron of honor. She planned my bachelorette the same day as my MIL “planned” a lunch at her house so I can give gifts to my bridesmaids. Back tracking a little.... when I spoke to her about having this lunch for the bridesmaids I didn’t NOT give her a definite time or date. She was the one who made an assumption. It is something that can be done the weekend before or after the bachelorette.... no big deal, right? Wrong. She threw a tantrum and said that she didn’t care anymore and that she was having palpitations (and she’s said that to me before, as if I don’t feel like shit enough). I’ve planned my entire wedding, my bridal shower, honeymoon, etc. (oh and BTW my fiancé and I are going to Florida for our honeymoon and she’s going on “vacation” with my father in law not even 2 hours away from us). I just need advice. I love her to death but I’m ready to throw in the towel. Also, my fiancé does stick up for me and comfort me a lot. He’s not home a lot of times that this happens though. There’s a lot more that happened but I’m upset right now so explaining it all will cause me to write a novel.