For a short time in act one of The Crucible by Arthur Miller, Abigail Williams and John Proctor are alone. This scene is most significant for its revelation that the two of them once had an affair, but it is almost as significant to hear Abigail speak truthfully to Proctor about the strange goings-on with the girls in Salem. She clearly speaks honestly to Proctor about how she feels about him, so we have no reason to doubt what she speaks about the Betty and the other girls.

Abigail tells Proctor what she thinks of Betty's supposed illness. When he asks her what "mischief" is afoot, she nervously says,

"Oh, she’s only gone silly some-how."

When Proctor tells her everyone in town is saying that Betty has somehow been bewitched, she says,

"Oh, posh! We were dancin’ in the woods last night, and my uncle leaped in on us. She took fright, is all."

Abigail wastes no more time on Betty, dismissing her cousin's foolish insistence on pretending with that simple statement. Betty is frightened because her father, the Reverend Parris, caught her dancing in the woods last night. She is acting like this to avoid any trouble--specifically to avoid punishment. 

Abigail wastes no more of her private time with Proctor talking about Betty.