The text of this brilliant play gives us no indication as to how Abigail Williams should be dressed, so we can only infer that she would have been dressed according to the fashions of her time, which, for women in a Purtain colonial America, did not leave much opportunity for choice or for self-expression. Women at the time wore a smple linen smock as an undergarment, several skirts that were referred to as "petticoats" which were made out of wool or maybe linen, corsets and jacket or a gown, made out of wool in a drab colour. Interestingly, black was a very expensive dye at the time and so was not commonly used. Lastly, women would have worn a linen cap and woolen stockings with leather shoes.
For a good representation of this, try watching the film The Crucible staring Winona Ryder as Abigail Williams. Arthur Miller himself helped to direct this production, and the clothing is accurate of the kind of dress that women would have worn.