I hadn't heard the expression gap year, but I guess that's what I did - take 4 of them. At the time I remember being very convinced that many more should do something of the sort. I don't know the corresponding age groups in the US, but I quit school when I was 16 to work as a jockey apprentice. I come from a family of academics, and felt that this was my only chance to try it out or it would never happen. I was sure that I would go back to school at some point though. Worked full-time for four years, growing up and out of jockey stature ;-) and went back to school. I was then raring to go and got top grades the first year. Dwindled a bit the last year before university, but I was still incredibly motivated and a lot more mature compared to my fellow schoolmates, who were for the most part just dragging their heels until they were "done". Many of them were actively considering re-doing subjects at a private school later on, to improve their grades...
Maybe it doesn't have to be a gap year, but balance is good for you, whether it's a part-time job or volunteering or anything else. If you or she can afford it I'd say go for it. I wouldn't think of it as a break, though, but as a chance to work doing something different.
Winter riding is much less about badassery and much more about bundle-uppery. - malkin
1995 Kona Cinder Cone commuterFrankenbike/Selle Italia SLR Lady Gel Flow
2008 white Nakamura Summit Custom mtb/Terry Falcon X
2000 Schwinn Fastback Comp road bike/Specialized Jett