I suffer from excess saliva due to the drugs that I am taking, But unless Reeva has been munching Lithium and antidepressants that probably isn't the cause.
I found this site which gives some more information ~
http://www.petmd.com/dog/conditions/mouth/c_multi_ptyalism but it seems that, lke me, you have a conscientious vet and they will try and get to the bottom of the problem.
I know what it is like - my moggies are my family and it is horrible when they are ill. I was at the vet with Frankie the other day and the vets and admin staff are all really good.
Good luck to you and Reeva.
Susan
mother of Frankie de Tom Cat
&
Merlin, Warrior Princess