Aspirin is commonly used for pain relief for dogs.
Call and ask your vet what he/she recommends as far as dosage and how often to give it to her. Make sure that the aspirin is buffered and you administer it during meal time to avoid stomach upset or ulcers. Also make sure that anything else you're giving her is not an NSAID when using aspirin as you don't want to overdose her.
Pet places generally sell aspirin that is geared for dogs. Probably pay a bit more for it though.
