She ought to, man!
Because, logically speaking, if your aim is to make sure your
schoolgirls are dressed 'decently' and not show off their
undergarments, then you ought to do stuff like make her wrap some
towel / scarf / whatever on top of her bra, so that the outline of
it won't be seen, y'know.
Or, make her wear some old-fashioned Made In China singlet
underneath the blouse to make her lao kwee, y'know! 
I mean, she's trying to be
'kewl' and making her wear that kinda singlet under her blouse is
like, biangz... super lian and no longer 'kewl' so I reckon that'll
freak them out more than going around bra-less, right? 
Besides, if some of them have this exhibitionist streak and wore
coloured bras so they could stand out, removing their bras will
make them lagi more visible and outstanding, which may be something
they've perversely wanted all along anyways!
So, the punishment she meted out, is really illogical, IMO!
