I'm so sorry to read about the problems your dog is having. I wonder why they even vaccinated a dog that age. :-(
Sounds like your Vet is doing what they can. I assume they have checked liver, kidney and pancreas functions? Those can be symptoms of problems.
Wish I could be of more help.
you might try looking up vaccine reactions in dogs (rabies vaccine) and see if you find any info.
It sounds as though the rabies shot has overwhelmed your dog somewhat. Dogs, as they grow older find it harder to cope with shots as they did when they were younger. Their immune systems get overwhelmed.
We don't have the rabies shot in the UK, but I understand it can cause a lot of problems.
For rabies shot reactions, this is a very good and informative site:
http://www.dogs4dogs.com/truth4dogs.html
However, it may be difficult to persuade your vet that the illness could stem from the rabies shot. Many vets either do not know about this or find it difficult to realize health problems (within a number of days or weeks fromt he shot) -can be related!
I don't know definitively, as I am not a vet, but it is just possible an antihistamine may help her. It is also possible a holistic vet who specializes in homeopathic treatment may help (if that is possible, as it sounds like your dog is hospitalized right now)