I think Abigail portrays quite a few characteristics, and she is able to change between them quickly, especially in Act I where she is all innocent at first, then she turns aggressive, and then flirtatious and then innocent again.
Abigail is a silly fool. She is completely unaware of the chaos she is causes. She does whatever she wants, whenever she wants to. During the Salem Witch Trials she had the power to have a lot of destructive potential.
Abigail is a chameleon, I'd agree. She is very good at manipulating people and seems to know how to quickly find people's weaknesses. There is a certain genius about her in this way, though it is used entirely for destructive purposes.
I don't know that she is ever actually innocent. She presents herself as being innocent, which is probably what you mean. She acts innocent when being innocent can help her. Then she acts viscious when that suits her.