Elizabeth was faced with a real dilemma. She could say, as she did, that she dismissed Abigail because she was "dissatisfied" with her. This is vague as it could mean that Elizabeth just didn't like her or that she was dissatisfied with Abby's work ethic. But then she admits that she suspected John of being attracted to Abby. She says:
I came to think he fancied her. And so one night I lost my wits, I think, and put her out on the highroad.
As the interrogation continues, the problem is that Elizabeth doesn't know that John has already confessed to the court that he did have an affair with Abby. She lies and says John did no such thing and is removed from the court.
Hypothetically speaking, being in Elizabeth's shoes, it would have been better to say Abigail "fancied" John rather than saying she suspected that John "fancied" Abigail. Citing Abigail's actions (rather than John's) as the reason to dismiss her would have been a wiser move because it would have thrown at least some suspicion Abigail's way.