Most puppies are born w/ round worms.
Yes the humane society should of treated her for them, but most treatments for roundworms in puppies is consisted of multiple treatments so most likely you would need to follow up with the remaining treatments. Every first puppy exam you should bring a stool sample or have the vet take one. Puppies are ussually treated even if it shows up negative.
You may not see them all the time.
Sometimes the dog shows no symptoms until they are heavily infested.
A dog can get parasites through many means & many parasites can be transmitted to your other dogs so if you think she them just grab a stool smaple & drop it off at your vets. They are cheap & so is the treatment for roundworms.