Troubles with Future Mother-in-law

I need some advice. My fiance and I got engaged in December, and ever since, I have seen a side of his mother that I had not seen before. As soon as we got engaged, she started talking to us about plans for the rehearsal dinner. I discussed some ideas with her and expressed how I would like a casual dinner. The food part of the dinner is complicated, though. I am on a special diet for health problems, and several of my family members have food allergies or restrictions. She eventually decided that she would have it at a fancy venue with a fancy dinner, and my family would bring their own food as long as we used her fancy dinnerware. I was okay with my family bringing food because I understand how hard it can be to accommodate our needs. However, I was not okay that she decided she wanted to do everything fancy. We had discussed that we wanted casual. Also, for our ceremony, it will be midday/afternoon and we aren't even doing a dinner for our guests. We are serving appetizers and such. Days went by and she sent my fiance and me a text with the menu for the caterer she decided on. She wanted us to choose which meals we wanted for the rehearsal dinner, except she gave us her suggestions on what she wanted. My fiance and I looked over the menus and did not like the options simply because we wanted something more casual. We expressed this to her, but she had her mind made up, and nothing we said made her rethink anything. It felt like I was backed into a corner. I knew what I wanted but it didn't seem as though anything I wanted mattered. In the midst of all the rehearsal dinner stuff, my fiance and I decided to make some changes to our guest list, resulting in a much smaller amount of guests, and cutting our wedding party in half because we want things to be more intimate and meaningful. Also, with a smaller wedding party, we decided we will not have a formal rehearsal, thus eliminating the rehearsal dinner. The day after, we decided to sit down and have a conversation with her and my fiance's father. It did not go well at first and nothing we were saying was taken into consideration. They initially said that they were paying for it, that they would not make any changes, and that they would have a fancy dinner whether we decided to show up or not. His mother yelled at us and started crying. I tried to stay respectful and calm but it was very difficult when nothing we were saying was being listened to or considered. My fiance went silent and I had to fight for myself. I tried to suggest an alternative thing that they could do instead of the dinner, like a brunch. I ended up walking away and had a panic attack. A little while later, my fiance came in and helped me feel better and then we had a conversation just with his father. He was understanding and said that we could go with the brunch idea. Which was strange because he was just yelling shortly before. He explained to us that my fiance's mother feels left out of all of the wedding planning. Fast forward to now, things have been tense ever since this interaction. Ever since we got engaged, his mother has asked a lot of questions about what the wedding will be like, how we will do things, etc. I am not a very traditional person but his family is and it seems like every non-traditional thing I like is looked down upon and I am made to feel like a horrible person if I don't do what everyone else does. I was feeling stressed with all of the wedding planning several days ago so I decided to sit down with my fiance so we could write everything that we wanted down so that we know what we want and we aren't going to let others change our minds. We wrote everything out and he decided he wanted to give a copy of everything to his mom. So he did. She took it personally and asked if we wrote everything because of her. We didn't. I even gave a copy to my mother. She said she might not even come to the wedding because of everything. Today I am still dealing with the repercussions of everything I guess. My fiance has decided that we should sit down with his parents and ask what they want us to do for the wedding. I am very hurt and upset and feel like my concerns and wants are not as important as his parents. I feel like I am very limited on what I can say to him about all of it. I feel like they are pinning me against him and making me out to be someone that I'm not. I think they have a lot of bad opinions about me now simply because I don't want what they want. What should I do? I am very frustrated and worn out because of everything. I didn't think wedding planning would be this hard or any of these things would be issues. If anyone has any advice for me, that would be greatly appreciated. I have talked with many family members and friends about everything and I constantly have heard that it shouldn't matter what others want for my wedding. It is my fiance's and my job to plan things and it is our day.