Mother-in-Law HELL

I honestly need input from y’all on this situation.
When I first met my fiancé he was living at home with his mom. He had just returned from Iraq and was changing military branches. I thought it was odd he was living with her, but didn’t say anything about it. Ever since I’ve known him he has never made an effort to talk to his mom, or have anything to do with her. (I’m the one that made sure he remembered her birthday, mother’s day etc.)
Our marriage is next month and his mom has spent the last 4 months trying to ruin it. I asked her in January after we got engaged for her list of people to invite. She waited until a week before we sent them out (in Mid April) to finally give me the list. She wanted the invitations herself and tried to get them, but since my parents paid for them and I was going to be putting wax seals on them I told her not to worry about it. As soon as the invitations were mailed out, she called me and was angry because “You didn’t put seals on MY invitations” (which Is a lie. I enlisted my entire family to help me do the wax seals and spent 2 hours doing them) Then, she said, “You didn’t put MY name on the invitations” which is news to me. Her son is a grown man. Regardless she had 4 months to say something and never did, my fiancé was in the store ordering them with me and never said a word.
She also “volunteers” to do things and then either doesn’t do them at all, or messes everything up. She actually tried to get people to donate money for the rehearsal dinner. She told the restaurant that we were going to have the wedding there.. when she knows good and well we are having the wedding at my church.
We have a set amount of food, plates etc. She went behind my back after I asked her nicely not to invite more people because we simply don’t have enough food, or wedding cake which I explained to her and invited more people to the wedding.
She also will play a manipulation game where if she doesn’t get what she wants from us, she will call my parents and tell them that we are “refusing” to give her information and what’s to know what’s going on.
She also wants to go on our honeymoon with us, and include his brother and the brother’s wife. Anyone else find that to be weird and creepy?
Basically, anything I do for the wedding she thinks that she can do better. She constantly accuses me of not doing things I did do ( like mail out her invitations, put seals on them, or even talking to her about our photographer) even when there are people around that hear and see me doing these things.
The problem is now, my fiancé is siding with her. The last 5 months he hasn’t said anything except “ignore her” now, he saying that I need to involve her more and it’s not her fault that she forgets things, invites more people when she knows its’ going to cause financial strain, complains about everything we do, and that she should be as involved as my parents.
I am the bride. She is not the mother of the bride, and she also ruins everything she touches.
I feel as though him sticking up for her is him picking her over me. I have not ever been rude to her, I just simply thank her for her input but decline her advice. Now, he blames me and says that she’s the innocent one and I’m the one who’s at fault.
I honestly am a nice person and just want an un-complicated wedding. The amount of complaining and manipulation she has done has made planning the wedding completely miserable.
What am I supposed to do? I feel like I can’t even trust my fiancé since he is picking her over me, and blaming me for her actions.