Who is Rosemary from The Memory Keeper's Daughter and what is their importance?

Rosemary was a pregnant teenager living in an empty, decrepit house in the country that belonged to David Henry. When David, distraught, visits his childhood home and finds Rosemary there, she very capably ties him up while he sleeps, just in case he is dangerous. Rosemary is estranged from her parents due to her pregnancy and is hiding here, taking care of herself with no heat or electricity. She cuts beautiful designs from paper, called scherenschnitte, a craft she learned from her Swiss grandmother. She is an intelligent and compassionate woman who listens without judgment to David's confession about giving up his daughter. She goes home with David and becomes a daughter figure to him. David is with Rosemary when she is in labor and, when he leaves Norah, he takes Rosemary with him to a duplex, where she and her baby, Jack, live next door rent-free. David supports Rosemary while she goes to college and is very sad when she decides to move away and start her life. She is grateful to him, and encourages him to tell Norah the truth about the baby.