AITA for asking my sister to wear one of the bridesmaids dresses I picked out?

I’m a bride currently planning my wedding. I just sent my bridesmaids the link to some dresses I picked out for their dresses. There are a bunch of different cuts, necklines, etc. for them to choose from because I wanted them to be able to find something at least close to what they liked. The only thing is almost all of them are sleeveless. My sister is expecting a baby about a month before my wedding. I knew that she would probably not be feeling her best by the time of my wedding, so I picked out a few styles that were maternity and post-partum friendly and that had short sleeves. My wedding gown has long sleeves, so I am trying really hard to avoid long sleeves on the bridal dresses. She said that she doesn’t want to wear any of the dresses I picked out. I pointed out that I will provide wraps for all of my bridesmaids in case they are chilly or want to cover up a little more, and the only time I would prefer they not wear them is during the ceremony. My sister says she doesn’t want to wear a dress that doesn’t have long sleeves and if she wears any of the dresses with short sleeves I am not allowed to post any of my wedding photos online afterward. I told her if she was really that uncomfortable with it she could always sit in the audience during the ceremony so she won’t be in any of the photos without her wrap on. This has made her irate and she is now saying that I’m being horrible and unreasonable. AITA?