An A level in dance is worth nothing in the job market or the academic market unless she wants to go to an arts school
This is incorrect.
I am a medicine admissions tutor and have taken students with dance A-Level, as long as they met other subject requirements (two scientific/numerate subjects). Unless the entry requirements page for the course says an A-Level subject isn't accepted, it is.
See, for example, entry requirements for physiotherapy at Manchester:
Grades ABB at A-level, must include a biological science (Biology, Human Biology, Sports Science or Physical Education are acceptable).
A-level Reforms - From September 2015, applicants undertaking A-levels in England in Biology, Chemistry or Physics will be expected to pass the Science Practical assessment.
We do not accept Extended Project or A-level General Studies.
DDD in BTEC Extended Diploma in any of the following: Sport and Exercise Science, Applied Science, Applied Science (Medical Science), Health and Social Care (Health Studies), Health and Social Care (Health Sciences).
We do not accept the following:- Sport, Sports Therapy Sports Development, Coaching and Fitness, Performance & Excellence.
Please note that we do not accept Applied Science as a single BTEC Award as it does not contain sufficient Biological content for this course.
The only thing I would query is whether they accept biology and PE in combination, but as they don't state explicitly that they don't they would be on very shaky ground legally if they rejected someone on that basis.
I would also question why universities keep referring to A-Level human biology and general studies, neither of which exist any more.