What was the immunotherapy for? Were you told what she is allergic to?
My old AffieX was allergic to loads of things, the only thing that ever worked for him was to change his diet to a vegetarian one

This was fine, until we were unable to get it any more :( After that we used Piriton after he had been on steroids etc for a few years with less and less effect.
Had we had access to the information available today, we would have been able to feed a
homemade diet, but back in the 80's we didn't have the info and were strenuously advised against it by the vets who thought it a very dangerous course of action

Back then labelling on food was very obscure, it was often difficult to work out what a food actually did contain so not easy working out what it was that worked ;)
Ridiculous when I think about it now, as dogs had survived and thrived for generations on scraps from the table in most families. But having the confidence of knowing what a dog needs and how to provide it makes a huge difference ;)