This sounds a lot like my 5 year old daughter. She chews on everything and even got a bald spot from pulling/chewing her hair. She cannot settle to sleep and can stay wide awake even past midnight. My son has ADHD and so do I, so I would not be surprised if she ends up having it too, but she is also starkly different from my son in a lot of ways. For instance, she isn’t forgetful and can follow instructions well. She also keeps eye contact and, while she’s messy, she knows how to organize and can entertain herself for a while with one activity. She is extremely wiggly and is always chewing on little toys or her clothes or hair and at one point was too afraid to be in a room by herself (even the bathroom!) She is afraid at night but doesn’t even settle when we lay down with her. She told me she can’t turn her brain off and has repeating thoughts (ruminating).
Her doctor diagnosed her with generalized anxiety disorder and sensory-seeking behaviors and described how she uses chewing and wiggling to relieve anxiety and calm herself. She also tics sometimes by clearing her throat obsessively but that comes and goes. She is currently on a low dose of Prozac, which has helped. We just went up on the dosage because it hasn’t helped everything yet and bedtime is still a struggle. The doctor also wants me to find her a therapist.
Hope that helps! Good luck!