Abigail wanted Elizabeth dead & Elizabeth knew from the very beginning that Abby wanted to take her place. Abby was always jealous, she did things out of spite and was quick to turn to violence,it only got worse after Elizabeth found out about the affair and fired her. Abby was drinking a charm made by Tituba to try and kill Elizabeth in hopes to get John Proctor all to herself. The chicken blood she drank shows her involvement with satanism &(or) witchcraft. Any person in their right mind would never drink blood. Later on in the book, we find out Abby claims Elizabeth is a witch and gets her arrested. She had no trouble calling out Elizabeth, she just wants her out of the way completely.