@bellinisurge It's not a problem at all. In the past I've had people e.g. want to film their normal group riding lessons and thinking that would get them good grades. It can be hard to know what to do, and schools aren't always able to give good guidance.
IMO, when the time comes, the best thing to do is to find an instructor who has experience teaching students for GCSE PE, or at least is willing to learn. If you can't find this, then second best is finding someone with experience of the BHS exams, as the riding content is fairly similar to the old Stage 2 exam- I know the BHS have changed their exams a bit too now though!
Unless you're very experienced yourself, I think it's hard to get a good grade without some outside help- a good instructor will be able to lay out a course of jumps to show all the required skills but also give horse and rider the best chance of being successful, for example.
At the moment (depending on your DD's standard) I wouldn't worry about things like the height of the jumps- that will come with time. However, if she can tackle a course of small jumps with balance and control, and do similar work on the flat (especially transitions, circles and serpentines) then this will give her a good grounding for whatever she wants to do in the future.