Ann is the daughter of Steve Deever, former neighbor of the Kellers, as well as former fiancée of the dead Larry Keller. A little while after Larry's death, she and Chris started writing each other letters. At his request, she returns to the Keller home, all grown up and beautiful. Chris wants to marry her, and she wants to marry him. They just have to figure out how to break it to Kate and Joe.
Ann may be young, but she knows what she wants. She's strong. She turned her back on her father when he was convicted of selling faulty goods to the military. She moved to New York and got a job. Visiting the Kellers, she has no problem going head to head with Kate, a fierce and manipulative woman who's twice her age. At the end of the play, when Joe's guilt has been revealed, Ann lays down the law:
"I'll do nothing about Joe, but you're going to do something for me. [Directly to Mother] You made Chris feel guilty with me… I'd like you to tell him that Larry is dead and that you know it. You understand me?" (3.86)
This is before Ann pulls out the big gun of Larry's letter. She's known all along that Larry is absolutely, positively dead – he killed himself – but she's merciful enough to keep quiet until Kate's stubbornness finally forces her hand. She also must have known that Joe was guilty. So when in Act 2 she warns her new fiancé, "I'm not here out of a blue sky, Chris. I turned my back on my father, if there's anything wrong here now…" what is she really asking? Perhaps she's just getting a handle on Chris's innocence or guilt, inspecting the goods she's about to invest in.
Ann's secret weapon makes her the most powerful character in the story, and the only one who reaches her objective – engagement to Chris – by the play's end.