Gross!
Tapeworms are from ingesting flea eggs. Make sure everyone is flea-free in the home and you shouldn't have problems. I'm guessing the SPCA treated your new foster for fleas before you brought her home? If you are concerned, you can take a fecal sample to your vet. I personally do not worm unless there are worms, with the exception of heartworm preventative. Tapeworms, while you don't really want your dog to have them, are typically not a huge deal (like heartworms).