If she got as far as the interview, she definitely is super intelligent and extremely capable in maths. It is a crapshoot.
If she achieves her predicted grades, she might have a chance to get into an American university for maths, but she's too late to get the application process rolling for the 2024-25 academic year.
If she wanted to take a gap year, prepare herself academically to do the necessary ACT /SAT exams, then do all the rest of the application process (College Board/ common app) and sort out a financial aid application for international students, she might have a chance of admission to MIT, Harvard, Amherst, Bowdoin, Dartmouth, Princeton, or Yale.
These colleges are "need blind", meaning all international applicants have an equal chance of acceptance, based on grades and whatever other criteria the admissions committees prioritise (extra and supra curricular activities might be important) and without reference to financial need (i.e. "[financial] need aware", which means colleges prefer international applicants who will be paying the full whack).
Obviously, the need blind colleges can be super selective, and "need aware" doesn't mean she wouldn't be accepted or that she wouldn't be offered financial aid.
Financial aid can be very generous at nominally very expensive American universities. A growing number of British students are choosing this option.