There could be several reasons that are causing her to itch...I suggest getting to your vet and having her checked...she may have an allergy to something such as her food - wheat and corn are BIG allergens to dogs (read your dog food label and also any treats you may feed her) these types of allergies are number one cause for itchy dogs....a hydrocortisone or lidacaine spray may help relieve itchiness (get at pet store) and bitter apple (also at pet store) may deter her from chewing since it tastes nasty but check with vet in case its something else....
Oh also could be fleas...
Oh also could be fleas...