M.B.
Has your daughter told you why she doesn't want to play? I know sometimes they can be maddeningly tight-lipped regarding their reasons..
My son, who'll be 5 in a couple weeks, so approximately the same age-range has been really enthusiastic about soccer, but has suddenly started to back-peddle on the enthusiasm, too. From things he's said this is largely a stage-fright issue. He wasn't expecting the rather large crowds of spectators, i.e. parents and siblings, that he now sees are in attendance. It's also a lot noisier than he expected it to be, and he's always been sensitive to loud noises- from what I've seen in his peers, this is a pretty common issue.
I don't know if your daughter's reasons are at all similar to my son's- but I've found that, breaking his objections down to smaller, individual issues helps us to address his fears and helps him to see that the problem isn't so large.
Good luck!
M.