Jenna (Jessie Mueller) is in an abusive relationship and works in a diner where she bakes her problems into her pies. She is planning on leaving her husband when she finds out that she is pregnant. She learns of a pie contest with a $20,000 prize. She starts saving up money and and hiding it around the house for the travel there. BTW she does all of this while having an affair with her gynecologist. Her husband finds the money and blows up at her. She tells him its for the baby's crib. She is left alone on the couch where she tells her unborn baby that the money that was used to buy her crib was the money she was going to use to buy them a new life and that they will not be going to the pie contest. Jenna then sings "She Used to Be Mine." It's very much about what neon said above. She sings about the person she was before life beat it out of her.