Ok I may have put things wrong here
You did give the impression that the root of the problem was Sebastian

I guess the vet has done tests on the skin irritation (scratched off a sample of skin to be tested) for mites etc?

These may help
http://www.nutrecare.co.uk/prod6.asp...0&msg=&offset=

or Rescue Remedy drops in her water.

Hope you get to the bottom of this