I have no idea what you feed her, but if you feed any pellet type foods, pull them out of the diet. It sounds like you have a pretty reasonable idea what your doing so I'm doubting that. There are a few things that can form thick saliva.. Renal issues and lung infection are among them. A blood chart will certainly help tell if she has declining renal functions. A good vet should be able to listen for fluid in the lung, feel for hardening kidneys etc too. If you need to see a vet that is not a specialist they still might be able to listen to the lungs, I imagine it would be much like listening to a birds lungs.. and the vet can give some antibiotics. Blood can be sent off but if they don't know how to read it, many vets know some specialists that do.. If not I know someone I can poke for ya... No guarantee on that though as this person is pretty busy I would imagine!