Thanks every one for the further comments.
I must admit, Maths appeals to me as as subject for the lesser amount of work. Like @Randomsabreur says, stuff like finishing a music composition would probably absorb half of DD's time!
@MakkaPakkasCave , thanks for the suggestions but I'm afraid not. She is hating History at GCSE unfortunately, and has no interest in Economics.
@ChiaraMontague , we did think of finding course-heavy subjects and, other than music (to a degree) there isn't much around like @clary says.
@StuckBehindtheTallboy , I think we are talking about the same thing really. Call them 'principles' in Maths if you like rather than 'facts', but in an exam DD can go blank, regardless of how ingrained knowledge was 5 minutes before. Such is the effect they can have on her.
DD does like Maths, she understands them and she says she finds them interesting. I myself find them dull as dishwater, but I have to believe her!
@Justasmallgless and @TizerorFizz , the 'bums on seats' trend rings true, sadly. However, it can sometimes have the unintended (but positive) side effect of allowing some students who are capable and will do well to get there in the first place. This could benefit children like DD, or my friend's daughter, who is doing fantastically at uni, top of everything, but only got there because her A levels were teacher-assessed during the pandemic, for instance.