
I think as well as continuing with vet investigations it might be worth contacting the breed clubs for both breeds to ascertain if there is a common gastric / digestive problem in either (or both)
Has your friend already tried a
strict exclusion trial diet - one source protein with one source bulk (such as rice or potato) and absolutely NO treats, titbits, chews etc during a four-6 week period? Usual first suspects to remove are wheat, gluten, corn/maize, dairy. The poor dog may have developed an intolerance to something(s) in its diet and offering random foods to encourage eating will possibly mask the problem periodically but could potentially worsen it over time.
Sorry to hear this - hope she gets to the root of things. Regards Teri :)