I must be missing something here.

Why do you think she is advantaged by having a non-STEM major, even if it results in a higher GPA?

You can be pre-med or have a bio degree, and then NOT go to med school and NOT pursue a research career. Many jobs that do not involve science respect or require STEM degrees. Many do not care what your GPA was, as long as it was not abysmal. Her GPA will likely not even be on her resume. But they will see that she was a Bio/Pre-Med major, which is generally an advantage. Many job posts look specifically for STEM majors.

Changing to a humanities major will NOT advantage her. I am confused about what you want her to major in, and why. If she continues to pursue pre-med, and she doesn't get into med school, fine. Don't pay for her med school apps. You are correct that it is unlikely (not impossible) that she will get in. If she is an underrepresented minority, she still has a decent chance, with good letters of recommendation and with a decent MCAT score.

Refusing to pay tuition makes absolutely no sense. It would only be logical if there were another major that she could change to that would open doors for her. For most opportunities (outside of grad school), her GPA is irrelevant. And in almost every instance, a STEM major is better than a humanities major for jobs.

Unless she has already taken a number of Econ classes and could switch her major to that, I do not understand your reasoning.