How to get the Crap off my puppy!?!?!!?

My grandpa recently bought Hartz ultra guard for my puppy because she needed a flea treatment because we go out into the woods a lot and i put it on her she used to be all happy and playfull and full of energy and now she dosnt like to do anything but lay down and is only eating a little bit of food i went to get it off her today and its mainly but her tail so i dont know how i can get it off without rubbing her sore spot and her being in pain and trying to bite me