Vivi, I think sometimes we go overboard trying to help our heavier students feel comfortable with their bodies and the really thin ones (who we wrongly assume don't have issues with their bodies) get hurt in the process.
Also, I've had a situation where I felt sure a heavy student was just so durned happy to have found an accepting environment that she wanted to play revenge games -- turn the tables, so to speak -- and take every opportunity to criticize dancers like the BDSS for being 'too skinny' to dance well. I had to set her straight that we're not here to criticize ANYONE'S body type, or exclude ANYONE. She stopped coming to my classes shortly thereafter, but I don't know if that was the reason.
Personally, I think we can all work with what we've been given. Juicier women often have powerful shimmies & stage presence. Very lean bodies really show off muscular undulations and flutters. *shrugs*