I know nothing about the pedagogery of the music...I've just sung the song. I always interpreted this as that she had given herself to her love before he left on the trip and perhaps even was pregnant as a result. Therefore, she could not longer wear "pure" petticoats and her parents tossed her out of the house.

She doesn't follow her love in the lyrics...she's waiting for him at home, so the idea of a camp follower doesn't fit.