My (20F) mom (48F) told me I can't be MoH in her wedding because she thinks I'm too fat.

My mom is getting remarried to the man she's been dating for the past few years. A year ago when they got engaged, she asked me to be her maid of honor. We've had a difficult relationship since I was a kid because of how she acts about my body which I'll get into in a bit. So when she asked me I of course said yes and was excited, thinking maybe she finally wasn't disappointed in me anymore. Their wedding is next month.
Today we (me, her, all the bridesmaids) had dress fittings. The dress my mom had ordered for me was 3 sizes too small. My mom made a big deal out of this in the store and kept asking me how much I weigh, how much did I eat to get so much fatter since the time she'd placed the order a couple months ago. I haven't even gained any weight over the past 2 months! She pulled a store attendant over to demonstrate how impossible it was to get the dress up over my butt and belly, pinching those parts and saying "is there anything you can do to deal with all of this?"
When they said they can't widen it and my mom would have to reorder a few sizes up, my mom then said this just "won't do" and she can't have me be the MoH anymore because it's "too embarrassing." She also said "Look at all the other women here and then look at yourself." She said if I can lose at least 40 pounds by then, I could still be MoH but how could I possibly do that?
I've always been fat, my whole ****ing life, and she has always been harshly critical of my body and it's really starting to destroy how I feel about myself. I got boobs quickly and earlier than anyone I knew. I was the only 5th grader who looked like an adult woman. She refused to get me fitted for a bra and just gave me her old bras. She constantly made jokes to sales people about how I was a "baby elephant" and couldn't fit into typical clothes for 10 year old girls.
Other examples: At Thanksgiving she grabbed my belly when I stood up from the table and said in front of the whole family, "WOW, you're certainly not wasting away even though you eat like we're starving you!". She's frequently stared at different parts of my body (thighs, arms, chest, hips) when I was talking to her. She would laugh about "how my double chin jiggles." Sometimes all this **** just makes me sick to my stomach and I can't eat. She then flips it back on me and accuses me of hating her cooking and never appreciating her because I'm selfish. It's almost as though she's oblivious of how hurtful her words are. She is also extremely critical of herself, calls herself fat even though she's very slender and fit, and thinks other people should do the same to themselves more so they don't get narcissistic. She constantly tells me "if I don't tell you how sloppy and horrible you look, who else will?" As though she's doing me a favor. She also judges total strangers and people on Tv, celebrities, models etc as either being "beached whales" or "looking like a 7 year old boy" (aka too skinny).
I've already tried talking to her and telling her she should be more body positive. She told me I was just trying to make excuses for being a hippo. Cutting her out is not an option until I finish school as she's paying tuition and I've come to realize there just is no point in trying to get her to see the impact her words have. I am anxious all the time visiting her on holidays. I don't know how to deal with her constantly making me feel like crap. I'm not really the monster she makes me out to be but lately I have caught myself hating myself and loathing my body. I have internalized all her hatred and don't know what to do about this mess. She sees me as nothing but a giant blob of fat.
TL;DR my mom told me it's embarrassing how fat I am after my dress didn't fit and she can't have me as her maid of honor anymore. What should I do?


Source.

Damn that's cold blooded!

Well crap that's sh!tty

I'd get drunk and grab that microphone. Oh, I'd make a toast for her to remember b.itch.es!!!!!