Bridesmaid Dress Woes

Hi all! So I had a question. Now that I know my wedding can actually happen it has me stuck on an issue that was moved to the backburner when the world was going through the heat of a pandemic. I have 7 bridesmaids, one of which is my FH’s sister who I love dearly. Unfortunately I am in kindof a stressful situation. My bridesmaids dresses are from a website that you can get many different styles in the same color and it’s $100 per gown. Not a horrible price in my opinion. I told everyone they could pick whatever style they wanted in that color from the site (about 12 options). When I first picked our colors and showed FH sister the site she had asked if she could buy a cheaper dress from a different site as long as she matched the color because she said she “wouldn’t look good in any of the options” (mind you she is model thin, gorgeous, tall, size 2, literally would look good in a burlap sack). I said yes not thinking (this was literally the day we got back from the vacation we got engaged on). About a week later after thinking about it I had second thoughts about how it would look because even if it is the same/similar color it might look different in different light, etc. so I told her I was sorry but I would prefer if she ordered through the site like everyone else bc of those reasons. She claimed it was a high price for a bridesmaid dress. Next thing you know we are at a wedding together earlier this year (about 2 months after I asked her to buy from the site) and the bridesmaids had on similar dress color as mine (looked identical) in a style she liked. She asked the one girl where she got her dress after the reception and the girl said “I don’t need it anymore you can have it” and literally gave it to her for free! And it’s her size. Mind you this is after I asked her to order from the site. Anyway I had swatches at home and it matched the swatch but I am concerned what if it doesn’t match in real life. Besides the point that she basically just ignored what I said I don’t want her to stick out in my wedding photos. I asked another bridesmaid to bring her dress to my future SIL house so we can compare- my big question is what do I do if they don’t match. Am I wrong for wanting her to just buy one from the website? Should I offer to buy it? Also for background she is not short on money by any means. She makes close to what I make and her fiancé makes lots of money like 3-4 times what we make and I know he wouldn’t mind helping her pay. I feel like $100 isn’t that much for a bridesmaid dress and she is tall so probably wouldn’t even need alterations. Am I wrong for wanting her to match?? Confused.