chewing

Hi all, I have a 9mth old Border Collie called Zoe who is chewing the white tip on her tail, theres not much left of it. I think she is doing it when she wakes in a morning and before I get up. She has toys but I can't give her food toys cos Mirk can be possessive with food, I spray her tail with Bitter Bite before she goes to bed . If anyone has any tips I would be most grateful. She is not stressed so I think it is just boredem.

perhaps it is an allergy?
what food is she on

Supadog sensitive