Heartguard is a preventative for heartworms. She can still get tapeworms by eating other feces or even by having fleas (grooming herself she can eat the flea feces).

So I suppose the answer would be yes, she can still get other TYPES of worms eventhough she is on the heartworm preventative.

And yes, dogs can hemorrhage but I would think there would be a lot more blood than you'd described if that were the case!