Future MIL attending wedding dress shopping?

So I'm going wedding dress shopping in a few weeks! I personally don't like shopping for clothes with people at all. I really only want my mum and my MOH there and Ive been excited to make a whole day out of it with them. But, now my MIL is asking to come. I don't get along with her very well and she hardly knows me or my style. She's not an easy person for me to get along with at all and usually my fiance acts as a buffer for us. She doesnt approve of me because of my religion, my belief in modern medicine or the fact that I don't let her take advantage of her son. She is always trying to squeeze her son for money and I really don't want her to know what the cost of this wedding is because otherwise she'll just get worse (our wedding isn't that pricey at all, but it's not cheap and my future in laws do not have a lot to start with).

So I don't want her with me when I look for my dress. I just want to spend the day with people that love me and support this marriage. I don't want to be dragged down at all. She's asked me repeatedly now when I'm going (she's basically assumed she's invited), but I've managed to avoid giving her an answer. I can't hold her off any longer. I haven't spoken to my fiance yet as he's away on buisness (no cell reception where he is). So I'm hoping you ladies can help me out! Should I just suck it up to keep the peace and maybe make her like me a little. Or just do what I want and know will make me and that day a happy one.

UPDATE: Sorry,I don't think I was really clear about my issue with her. My issue isn't her opinion on the dress at all. I don't care what she thinks of it and Ilmnot worried about her negative comments about the dress. I'm worried about her knowing the cost of my dress because while my budget isn't huge, if it's over $500 (which I'm planning on it being based off the style I want) shell have her hand out to us for more money (she'd take it all from her son if she could). And I really don't want to hear her rude comments about me as a person (and as many of them will apply to my mum it'll suck for her too). The dress I can handle it's her usual crap that I don't want on that day. I've been trying to build some kind of relationship for 5 years and the more I think about it the less and less I want her there. Also this is my ONLY chance to go with my mum as she lives in another country and I can't pick a dress without her.