University admissions tutors know their subjects and their cohorts best, and degree programmes have developed curricula and pedagogies to fit them.
Pupils and students develop intellectually at different rates. DH struggled a bit in his first year at Cambridge Maths, did not get First Class results until Y3, achieved a Distinction at the notorious Part III, turned down the offer of a (funded) PhD position there for a different one, and has recently retired from a career as a Maths professor at highly ranked universities that was full of esteems.
Yet when I once wrote on a thread here in commiseration only that he had struggled a bit in Y1, others were quick to jump in and say perhaps he had overreached and didn’t really belong at Cambridge.
I think a bit of that may be happening here. OP’s DD just got 96% on a Maths test towards the end of Y12. That’s mastery. We don’t really know what happened earlier.
Glasgow, Lancs, Notts, Loughborough, Liverpool, etc all produce many fine mathematicians. And if the DD here was in fact thrown by a discrete issue, like finding unexpected material on her mock, she may well have underperformed. I wouldn’t like to be examined on A level Statistics without brushing up, either.
PS Liverpool is RG and Bath and Loughborough are RG+. Leicester may be also but sadly its Maths has been essentially subsumed.