My sister was supposed to be maid of honor in my brother's wedding several years ago, but a few months before the wedding she asked to be demoted to just a bridesmaid. My sister-in-law (the bride) said okay despite being hurt by this. I stepped up as maid of honor in my sister's place. My sister is the one who suggested I take her place. Fast forward to a few days ago, my sister was asked to be matron of honor in a friend's wedding. She excitedly agreed despite the fact that she backed out of that duty for my brother's wedding and was essentially a maid of honor in name only in my wedding. She refused to do a speech, I bought her dress because she refused to wear the original dress that she bought, and she didn't help with planning the bridal shower or bachelorette party. So while it is hurtful to both me and my sister-in-law because of how she treated us when we asked her to be maid of honor in our weddings, we have accepted it for what it is.
The problem now is that the bride in the wedding she is matron of honor for told my sister the matron of honor and bridesmaids can wear any blue dress so my sister wants to wear the same exact dress she worn in my brother's wedding since it is blue. This has deeply hurt my sister-in-law. So do you think it's wrong to rewear a dress you already wore in one wedding?