Answer:
Abigail Williams drank a charm to kill Goody Proctor because she was in love and obsessed with John Proctor. By drinking the charm she could assure John Proctor's wife would be dead so Abigail Williams could have John Proctor all to herself.
Step-by-step explanation:
In the Crucible, John Proctor and Goody Proctor also known as Elizabeth had a unstable marriage and relationship. The reason their marriage was unstable was because John Proctor had committed lechery. A while back, Abigail Williams used to work for the Proctor's until it was discovered John Proctor and Abigail had an affair. So Abigail had loved John Proctor so she decided if she drank a charm that it might get rid of Goody Proctor.