Would you ask her to step down from being a bridesmaid?

So I'm having a small wedding- only family and the bridal party (total of 50 people). My maid of honour is my best friend and another close friend is one of my bridesmaids. The other bridesmaid is my fiancé's sister. I picked the dresses, they are a fuchsia pink, cover shoulders and are a couple inches above the knee. They have matching shoes with a 1.5 inch heel. They're modest and church appropriate dresses. I love them and my two friends really like my choices too. Besides the dresses (which I'm paying for) all I've asked for is that they have minimal makeup and their hair a certain way (I'm also paying for their hair and makeup). The hairstyles are very simple half-up/half-down. That is it. Of course my friends have gone above and beyond to help me plan my wedding as well and helped my mum throw my bridal shower and thew my stagette. My fiancé's sister has done nothing and I haven't asked her too.

But she's making a huge fuss about wearing pink. She wants a long dress, she wants her shoulders showing, she doesn't want to wear heels (this is coming from the girl that only wears heels- I've never seen her in anything but 4-5 inch heels), she wants make up that in my opinion is way too heavy, and she wants her hair up in a really fancy up-do which is more elaborate than how I'm having my hair done. She's fussing about everything! She's even starting to make comments on the wedding itself and how I'm making it too fancy (the budget is pretty low, but since there's only 50 people we can afford it- we only invited 24 people they all have plus ones and myself and my fiancé are included in the total 50). I don't want her in my wedding party! I have a friend that would fit her bridesmaid dress and has recently become available at the time of my wedding. I was originally asked my friend, but due to personal things she wasn't sure the date would work so asked to just be a guest. It wouldn't be hard to make her a bridesmaid now. But this girl is my fiancé's sister. He said he doesn't care what I chose and I believe him (he's talked to her a lot about her behaviour actually). Would you ask her to step down and replace her with a friend that would very happily be a bridesmaid??