The dress is too small. Look at the waistline and arm pits. The "idiot educrat" let her into the prom because she could cover up with the shawl. She chose to leave after an hour. The school made an exception and let her in.
It’s strapless, it has to be tight enough to hold itself up.
I do think the percentage of boobage showing is probably proportional to a much smaller endowed prom attendee who got to show her 40% without being embarrassed. Still think it’s a shame someone started all this hoopla.