Who is Dr. Sara Lowenstein from Lullaby: A Novel and what is their importance?

Dr. Sara Lowenstein is a radio doctor. She counsels the people who call into her radio show. One day, Dr. Sara was extremely rude to a young pregnant woman while Streator is listening to the show. Streator thought about the culling song toward Dr. Sara, and suddenly, the radio suddenly went silent. Streator was surprised to learn that he could kill someone who was not even near him.