She could be suffering from a mineral or vitamin deficiency, I would get her tested. Also consider bach remedies and/or homeopathy. See a doctor and/or naturopath before it gets any worse and the habit has been formed for too long, the longer you leave it the harder to break.

I agree with Mirlie !

i would talk to your GP and see if there is any underlying issue here. but it also could just be habit.

I think it’s anxiety related too. Perhaps speak to a doctor.

Sounds a bit like anxiety. My daughter used to pull her hair out (from birth almost) despite only really having fuzz for almost 2 years. She still plays with her hair on occasion, but I’ve learnt it’s when she is feeling unwell, stressed, tired, overwhelmed, nervous, etc. At this point, you can start discussing it with her and talk to her about how to express her feelings and other ways to manage those feelings. I read books about emotions (“When I’m feeling… by Trace Moroney), I did emotion puppets, found emotion crafts for toddlers on pinterest. These helped her identify and then communicate her feelings.