There's certainly nothing morally or ethically wrong with a woman wearing a kilt. Pipers do it all the time.

Problem is, they look funny! I noticed some time back that women and men are built differently (ooh la la, vive la difference!), and that difference means that if one of us wears clothing cut for the other gender, it tends to look odd. Look at a woman wearing a man's trousers some time. The . . . uh, parts, don't fit the same way in the same places. (Is it getting hot in here, or is it just me?)

If she wants to wear a kilt, tell her to go for it. No one will care any more than if she wore her father's overalls or sport coat. But she'd probably look better in a woman's kilted skirt.

It's no more important than any other matter of taste in the big scheme of things.