It would help to know how old your daughter is.
Offhand, I would say yes, let her quit. The motivation really should come from her. (That said, my son once wanted to quit clarinet, and when I said that was fine, he put his hands on his hips and in an outraged voice said “Mom, you’re not supposed to say that!” I would say, though, that from that moment on he was more committed to clarinet, not less, because it was his choice to stay.