Indoor cats are not necessarily bored cats.
If there is nothing physically wrong with the cat, then it is a psychological issue. It is difficult with cats to figure out what is bothering them, but you friend should carefully think about what is going on in their life. Did something change in the family (ie: family member off to college, new boyfriend/girlfriend around, is less time being spent with the cat...) - the problem usually lies in some change, and it can be subtle. Overgrooming in cats is usually from stress.
PS - is the vet a feline vet? If they are experienced with cats, they should have introduced to your friend that if it's not physical, it's probably psychological.