I think she's a little too old for an exchange plus that seems an unproductive period of time (has worked the past three summers and would want/have to work this summer to earn and to keep up her cv).
She will be 18 in August but any jobs (au pair, etc) abroad are for over 18's.
I can't think what else she might do. I believe that total immersion is a great way to learn a language but how can she do this when she kind of falls between two stools?
I'm hoping I'm being a bit thick about this and there are obvious solutions out there..