Don’t know what I’ve done for her not to like me 😔

I have no idea why but my mother in law doesn’t like me part of me feels like because my husband and I married so young and she just didn’t take us seriously so didn’t bother making me feel welcome in the family. I’ve done nothing but love her son and her family more than life. I’ll give you some back story so I met my babe when we were 12 and we’re bestfriends straight away we just clicked and then life got in the way different schools different Suburbs different churches and we didnt see each other for about 3 years then I went with a friend to her youth which was the same youth and we both kicked off where we last left 2 years later we started dating and 2 years after that we got married almost been married 3 years now and have a 1 year old. Anyway I always feel like she goes out of her way to make me feel unwelcome when we were dating and the odd occasion she would actually invite me for dinner she would make it so I couldn’t eat it and have to buy my own food ( I’m gluten free) so she would make stuff like pizza and not even bother getting me a gf base or even text me and ask if I could bring a base and I would ALWAYS ask if I could bring anything oh I also cooked her and her family dinner a couple months ago. She does things super subtle and I don’t really want to lay this all on my husband as it is his mum and he adores her. I feel like if I were to approach her and confront her she would think I’m just causing drama and she just wouldn’t care. She never got me anything for our engagement, kitchen tea, wedding or baby shower in fact it was hard enough just to try and get her to help out. But now one of her other sons is getting married now the thing is, everyone is questioning my brother in laws motives, he’s late 20s and very very vein cares a lot about image and this girl isn’t attractive at all (for someone he would usually go for) but she comes from a very very wealthy family her dad has already bought them a house outright as a “blessing” and is paying for their wedding, literally everything I would say it’s at last $80,000. His dad is also not convinced it’s legit like you watch them together and there is 0 chemistry I feel sorry for the girl because she’s nice but it all just looks like a set up for himself and he is so like that-would marry for money. But my MIL has also taken her out for lunch and coffee took her to an expensive pizza place when all the boys were at the pub now every time the boys would go out before I had a child I would wait for my husband at his parents and she would hide upstairs in her room and not even talk to me oh and the best part in all this is she bought her stuff for her engagement party, kitchen tea and said she’s going to buy them a box of wine from a high end winery for their new place, we live in a tiny house my living room has turned into my sons room cause our room could barely fit a bassinet. Like she’s great with my son and I’ll drop him off when she wants him and she’ll ask if she can have him but it’s always to benefit her and not me. Like I don’t know if it’s my image because my mum mentioned something to me, since having a baby I’ve gone from size 8-10 to a 12 and am actually feeling really down about it (MIL is tiny 6) I recently wore a fitted dress for my brother in laws engagement and I actually for the first time felt great in it, everyone loved it. When I saw my MIL I said “ wow that dress is so nice I love that colour on you” she said “oh hah thanks” and that was it and I was just thinking ok I know I look fab too you don’t need to tell me lol. Then later that night one of my other brother in laws comes up to me and says “man ...(bride to be) brother is so rude he comes up to me and says wow ...(me) looks pregnant and I just said to him “that is the worst thing you could say to a women dressed up, then I just walked off” I felt so self conscious for the rest of the night then when I was talking to my mum recently she said my MIL mentioned to her that I didn’t look classy that night, I was wearing a navy blue lace dress that came to my knees. My mum then proceeded to say I’m not going to tell exactly what she said cause you’ll get upset but yeah she didn’t like you in that dress. Mum and her are really close. Sorry for the splurge I guess I’m just feeling really defeated and really hurt as I know I haven’t done anything wrong. I don’t know what to do or how to feel better literally thinking of starving myself to get her approval