Think of a pianist who is accompanying a violonist. What would you call the act of playing music and adjusting your tune, melody and playing to the musician you are accompanying. So the word accompanying is used a lot, but it's not specific enough. Accompaniment means a vocal or instrumental part that supports another, often solo, part, but it doesn't tell you that it's done particularly well and with respect to the tune, melody, playing.
Her piano ___ the playing of the violonist.