SleepyHead, just bear with it for now. It happens in all schools, comprehensives and grammars, simply because children come from different primary schools and different level of knowledge and the teachers need to make sure everyone is up to the same standard. From year 8, a lot of schools set them for maths, so the problem should disappear.
I think Amber is right in saying that you may simply end up creating the same issue for the future if your daughter races ahead with the curriculum.
If you want your DD to do some more challenging work, I wouldn't go for GSCE books, but do something like maths enrichment instead, i.e. work with the skills/concepts that she has already learnt but try to get her to do various math challenges. You can find those on line, but if you need more suggestions, it may be worth posting a question in the Maths section of the forum.EDIT:
sorry, Guest55, just realised I've cross-posted with you.
You have your solution now, SleepyHead