I've got an undercut - less of a style statement of any kind, rather that I have really thick long hair and this means there's less of it to deal with.
DD (who's 11) has very thick long hair too, and wants the same for the same reasons (she loves her long hair but there's so much of it to wash and dry which I completely sympathise with).
I don't have an issue in principle with her having it, but think we'll look a couple of idiots walking down the street with the same hair if we both have it done? I'd never consider us wearing the same clothes so AIBU in saying no to this?!