It really doesn't matter PY. It has no impact on her GCSEs. The rationale of doing SAT in Y8 is that they will have 3 year to do GCSE courses, so should theoretically do better.
I know as a science teacher who completely disregards SATS, is that I easily do much of the GCSE course in Y9 because that is the natural and appropriate place for the work to be. I don't have the frustration of spinning my wheels in Y9 waiting for time to catch up with my pupils' eagerness to move on.
level 8 is the highest they can do ds1 has been on 8 since yr7 as he is maths boff he is still on 8 and his progress grades are always 1 Your dd sounds very bright paula they must think she is very capable?
i think they think she is good at maths and are pushy as its all girls state and they like good results i am fearful she will compare herself to her brother who took sats normal age and not fare as well i dont really care - but school being very forceful