Dewormers *can* cause icky weird poos, so hang in there - it's probably just her system purging the worms. If he saw an actual tapeworm, she likely didn't think it was necessary to do a fecal, though many vets might've done one just to make sure nothing else was going on. Keep an eye on her, and keep her bottom clean/dry. Call vet in a.m. if she is still having issues, never hurts to call.
