Some pianists have a misguided view about what is “suitable” for ballet class (e.g. that you have to improvise in a pastiche classical style with no dynamics and no rubato, or that dancers don’t listen so there’s no point in playing your best). This often happens as a result of teachers giving (or appearing to give) too much guidance as to what kind of music they want. Give your pianist an opportunity to play what they like playing, the way they like playing it, and you might find that it’s nearer to what you actually wanted in the first place.
As an example of this, a teacher once told me of a summer school class she was teaching, where the pianist never seemed to play quite what she would have liked (I think it was pirouettes that were the issue). It didn’t matter what she said, the music was never more than OK-but-dull.
On the last day of this summer school, all the teachers went to the local hostelry for a bit of a knees-up, and there, as chance would have it, was the pianist from the class in his other job, entertaining the drinking public from the piano. And there, at last, was the music this teacher had been trying to get out of him all week.
The moral of the story is, if you’re teaching on a summer school, go to the pub on the first night.