I currently have two staffies and they always do the same thing.
Although just to clairfy, is it "biting" biting or more of a licking and sucking?
If so this is because staffys are really sensitive to many backyard plants and weeds.
It is common for a staffy to bite/lick their paw, scratch there ear.
You can simply buy some cream or antibiotics from the vet to sooth the rash or allergy.
If it is just general biting maybe she is feeling bored or entetraine dlike a dog would chase its tail. If so simple buy a new dog toy or maybe think of introducing a new dog into the house!
Hope i could help