I just did a search and found this message and am amazed because my 5 year old is the same. She is also very confident and happy and aswell loves to fiddle and can't sit still (loves stimulation).
We have just given her a baby blanket to chew on at preschool and with the help of her teachers are encouraging her to only chew on that with the understanding that this will be taken off her in time when she learns to stop the habit.
Not sure if it will work but are giving it a try anyway.