My Cat Chews Her Tail, Could You Tell Me What Causes Her To Do This?

Have your cat examined by a veterinarian-there are medical and behavioral causes for self-mutilation.
Parasites-like fleas, ticks, or mites, ringworm, a wound, allergies, or a metabolic disease can lead to overgrooming/self-mutilation.  Your veterinarian will do several skin and blood tests if appropriate to find the underlying cause and then treat it!
Obsessive-compulsive issues, anxiety, or stress can lead to overgrooming behaviors.  Alleviating causes of stress can help.  Some cats need behavior modifying medication to stop overgrooming.
Good Luck!

If the cat nibbles on it for about 30 seconds and goes back to what she was doing before but maybe a while later she goes back to nibbleing, she might have fleas or a small tick stuck there and she is trying to get it out or it could be a rash.

Maybe a rash or tick