Not reported in this story is that the girl had a shawl with her and the school told her to wear the shawl.
She refused to comply and instead, left the prom and went home.
As near as I can tell, there's no rule that says that a prom dress must be low-cut and/or strapless. The choice of attire was hers.
Case closed. Just another idiot wanting attention. Whaaaaa, look at me!!!! Our school has a dress code. Everyone knows it. It's in the handbook which parents and students have to sign every year. Girls can't go strapless and can't have their boobs falling out during class or during prom. Two of my daughter's gowns didn't have straps so I cut a strip off the shawl and sewed on the required 2" width straps on one. For the other, it was just the small matter of digging through my sewing stuff and finding some similar fabric to make straps. It's not rocket science to attach straps nor does it take any effort to buy one that meets the requirements.
I don't have a problem at all with having a dress code. We were at the mall once on prom night (not our school) and you wouldn't believe what the trashy hoochie mamas were wearing... or not wearing. Dress fronts literally cut all the way down to you know where, ick.