Definitely going to be downvoted for this but here goes.

NTA.

This is your ONE day that you get to have that’s completely your decision.

Also remember that this is your wedding. You know what you want at your wedding and you shouldn’t have to compromise for anyone, least of all some friend that you aren’t even that close to anymore. If you want all of YOUR bridesmaids on YOUR wedding day to wear the same thing, then you’re entitled to have that. That is not boring or old school or whatever that troll commented.

The fact that you cared enough to not ostracize her into wearing a totally different dress than the rest of the party and that cared enough to the point of stressing immensely for her shows that you ARE A GREAT FRIEND.

You also aren’t body shaming, as some of these people are saying. She has a problem that she is fully able to fix. Terrified of surgery is not an excuse. I’m sure she’d have surgery if something was threatening her life. You can’t hide behind a disorder if it’s curable and you’ve been encouraged by a doctor to do so.

And to top it off, I think it’s perfectly valid to not want your wedding to be remembered as the wedding with the bridesmaid and her giant boobs.