I wouldn't say it's vain, or that your situation is any less valid than anyone else's.

[ Anyone who's had any part of their body, significant or not, turned into glass has a right to be upset about it and want it back to normal, as far as Cortana is concerned. ]

Yours may not be as dire a situation as others, but you still have a right to want it fixed. Besides, it's not as though we can't be sure parts of your scalp haven't been turned to glass along with your hair. It's safer to leave it as is than getting rid of it.