I would compare her crop to the rest of the chicks before I treated. My chicks in a brooder never seem to stop eating overnight to ever have empty crops, LOL. Maybe try putting the affected one in a little shoebox with only water and no food, but still under the heat lamp with the others...
It is normal for chicks to have full crops after eating. Is it abnormally full and hard? Does it go down at all? Is the chick on pine savings? Sometimes when they are little they will eat the pine shavings and get an impacted crop. You can put them on paper towels or sand for awhile to get...