The one thing we are certain of from the moment Arthur Miller introduces us to Abigail Williams in The Crucible is that she is a liar. He says she has "an endless capacity for dissembling," and we know she has already lied about what she and the other girls were doing in the forest last night. We should not be surprised if she keeps lying. Abigail has two motives for lying, and they are the same motives she is likely to use for accusing others of witchcraft.
Her first motive is to save her own skin. She does not want to get punished for being in the forest last night; she is even more worried about being punished for engaging in witchcraft, which we know she did. Abigail threatens the other girls and lies consistently to everyone in this act--except John Proctor. She tells him the truth: Betty is sick because
[w]e were dancin’ in the woods last night, and my uncle leaped in on us. She took fright, is all.
Abigail's equally strong second motive for lying is to get what she wants, and it is clear that what she wants is John Proctor. In fact, she had a relationship with him for a time, but John broke things off. In the woods last night, she did something awful to try to change that.
Abigail, pulling [Betty] away from the window: I told him every-thing,' he knows now, he knows everything we--
Betty: You drank blood, Abby! You didn’t tell him that!
Abigail: Betty, you never say that again! You will never--
Betty: You did, you did! You drank a charm to kill John Proctor’s wife! You drank a charm to kill Goody Proctor!
It is clear that Abigail will tell whatever lies she must both to save herself from punishment and to get what she wants. Given those two things, it seems likely she will soon be accusing a Proctor, either Elizabeth Proctor (so Abigail can have John) or John Proctor (as a punishment for not wanting to be with her any more). Perhaps both.