"An" in Shakespeare's Taming of the Shrew

In Act 1, Scene 1, Katherine says to Bianca "A pretty peat! It is best / Put finger in the eye, an she knew why".

I understand "Put finger in the eye" means she is fake crying for sympathy, but what does "an she knew why" mean?

I’m guessing that "an," somehow means "if," since this makes the most sense.