Ask her if she knows for definite what she's doing afterwards. Has she solid plans of what she's gonna do?
Has she really thought through what she wants to do, and exactly how she's gonna do it?
Or is she just dropping out cos she's being childish and can't see the benefit of it?
At the end of the day, if she wants to mess her life up, that's her choice, but perhaps making sure she has definite plans of what she wants to do, and how she's gonna do it (i.e. she's not just dropping out so she can do nothing all day or because she's "fed up"). Make sure she has a career plan, and not just throwing her baby out of the pram cos she's finding it a little hard.