I used to teach kindergarten and would occasionally have a student who did this. They would chew on pencils, paper, even their own clothes. I think at this age it could be more of a nervous habit than anything else and maybe it calms her down. Does she always do it? Or do you notice it more in situations where she might be a little stressed (like when she's in trouble, getting dropped off at DC, etc)? My only idea is to maybe to give her something to hold that she can fiddle with instead of chewing on things.