It must be so frustrating not being offered the language of her choice.
If they really can't fit her in the Spanish class, then definitely take the offer of both languages. I know she doesn't want to do German, but it is only for a year. The advantage is likely to be that she'll be with other bright students, so the lessons will move at a faster pace (and not be disrupted by students that have no interest in learning).
Then she can drop German next year and carry on with Spanish.
Your other option, if you're really dead against her doing German, is to ask if she can work on her Spanish in the library whilst the German lessons take place, and so just do half the lessons on the timetable i.e. the Spanish ones. School are pretty unlikely to agree to this, but worth a shot.
However, German is a fab language and I personally love it, so I would say do both, and at least she'll learn something new next year. I'm still a big believer in learning for learning's sake. Life's not all about exams and qualifications.
And off topic, but I'm astonished at Hopping's view that German is useless. Professional translations for example are done by native speakers, so there's a huge Ger -Eng market out there, precisely because Germany is such a huge trading partner of ours and has such an important economy.