She is shown to be a bit off off with signs of lucidity as when DCI Tom Barnaby questioned her asking her where her mummy is? She responds "Do you think I'm simple or something?" But when he asks her how old she is, she says she's 12. She has a dog named Doggy, or rather that's what she calls it. Willow is a little scared at night and goes to sleep with her dad but finds Jeannie Harding with him.
Her mom is Ingrid Peterson. She and her dad visit her at 5 o 'clock. Willow makes straw dolls and shows it to her. It is possible the reason why Willow is off is because her mom's prior drug use affected her.