I think sitting maths gcse early is absolutely fine if they are likely to get 8 or 9 on the whole thing (was this one paper, the full gcse is typically 3 papers, or 2 longer ones for igcse). AND, and this is the important bit, if they get to continue making progress in their maths. Following through with additional maths, and a plan for after that if not ready for a levels, and keeping doing the maths challenges, moving into olympiad problem solving.
I would also strongly recommend ensuring she is being encouraged and extended in physics and coding skills.
She might also be interested in the national cipher challenge which has just started so is one to look up straight away.
My eldest did maths GCSE in yr 10, add maths in yr 11, which worked well for her (and i think they kept the cohort together for a levels apart from those doing further maths as well). She had a great science teacher in yr 7 and 8, and in retrospect wishes she could have done physics gcse early as she feels she didn't learn much more after that ... By contrast my youngest is at a school that doesn't do maths gcse early but does ensure they are extended thoroughly in maths and sciences as appropriate; I don't feel that he is missing out by not doing an early gcse.
OP I really hope your daughter can continue to be stimulated by maths, it opens so many exciting doors if you enjoy and are good at it!