I don't believe under the new system that there will be a "foundation" and "higher" GCSE paper, just one exam that all students will sit
For maths there are still two tiers under the new system.
Surely only the most gifted will be doing the higher tier?
I don't think that's true. If it were true then the papers won't be fit for purpose. From reading threads (especially those posts from @noblegiraffe ) it seems to me that this year schools are being conservative over borderline students, and putting them in for lower tier whereas before they might have gone for higher. However I would have thought that any child expected to get a solid B at old GCSE would be put in for higher tier still.
Additionally, depending on the size of your school, I see no reason why a top-of-second-set child wouldn't be aiming for a GCSE 6 or 7 anyway and thus no thoughts of a foundation paper at all.
By the time your y8 gets through to GCSE the schools will have had more experience with the new style papers and should be on top of it all.
Furthermore, as long as she gets the 5 for maths (low B in old money) I can't see universities being too bothered on the grade if she is doing humanities subjects. The A level grades will be what they are looking at.
In summary, try not to panic. (My credentials, maths degree, DD1 did GCSEs in 2015, DD2 in y7)