Why do MIL have to make things so hard!?

I have always been kind to my future MIL. I have always tried to be helpful, considerate and respectful. I've tried so hard for the last 5 years to build a good and healthy relationship with her. I'm the one that reminds my finance about calling/visiting her and buys flowers/gifts for her on mother's day, her birthday, Christmas, etc because my fiance is so incredibly forgetful. Its all me and she knows it because it's such a massive joke between his siblings that if it wasn't for me my fiance would forget he had a family (he's an amazing guy with great intentions but he's just forgetful). Yet my MIL never appreciates anything I do, is always disparaging about me and is always doing something passive aggressive to hurt me.

Today, I discovered she's invited an extra 32 people to my wedding including plus ones! That's an additional 64 people invited to a wedding that is planned for 100 guests plus the bridal party (110 in total). My fiance and I each got 15 invites, my parents got 20 (they are paying for the wedding so my fiance and I decided they could have the most invites) and his parents got 15. Everyone also has a plus one. The venue and church are booked and the venue will not fit more than 120. And that's a few thousand dollars extra for food and alcohol too and my budget is already almost maxed out! I'm furious! Her excuse is that their family is bigger which isn't even true as both our families are very large!

She also showed me her dress she'll be wearing and it's the colour and a very similar style of my bridesmaids dresses! That's the one colour besides white that I asked no one wear! She's seen the dresses so it's not like she didn't know either. I swear she's doing this to hurt me. And she's demanding she gets to come dress shopping with my mum and I and my mum and I have always wanted my dress to just be between us ever since I was little. I just can't take it. I love my fiance and he's off trying to reason with her. But I honestly don't know if I can do this for the rest of my life. She's been doing this kind of thing ever since I showed up in her son's life. I've always tried to be the bigger person hoping shed come around. But now I just want to cancel everything before she ruins more of my wedding. Why does my finance get great in-laws and I get ones from hell?! Why is it always the mother of the groom that has to be evil?!

UPDATE: I sent the invitations last week. She's made her own and sent out these additional ones!