How does Miller attempt to establish Abigail's motives by changing her age and emphasizing that she is an orphan?

I think that he tries to muster some sympathy for her. She is 17 and still immature. Is she seeking attention rather than being down right nasty? Miller wants us to wrestle with her motives throughout the play.

Also the fact that she really has no parents gives us some amount of understanding. Is her crush on Proctor a father figure thing? We do feel a little sympathy for her until she gets down right crazy vindictive during the witch trials.

What was the girls age? and How does miller attempt to establish her motives in reality?