I know that a person can't change unless they want to, but how else can I convince her that dropping out is a bad choice?
She must be tired of hearing the same things over and over..
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.