why does betty know that abigal didnt tell Parris about the blood?

Abigail drank blood and cursed Proctor's wife.... she drank the charm to bring about Elizabeth's death. Abigail would never had told Parris because he would have forced her out of the community. I doubt Parris would have done anymore because it would have blackened his family's name. His main concern would have been to distance her from his family and position.