Sometimes they get tired of the same-old-same-old and hold out for something new. Could that be it?
Does she show receptive coloration? Perhaps she's wanting a mate?
My sister is a registered nurse and says that she learned in college that it is normal, throughout the animal kingdom, almost without exception, for members of every species to occasionally fast and purge. That pet owners should not be concerned when a pet does not eat for a day or so, if everything else appears normal. Don't know if this is necessarily true of chameleons, though.