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

Dr. Sara Lowenstein is a doctor with her own radio show. When Dr. Sara is extremely rude and patronizing to a young pregnant woman on the radio, Streator thinks the culling song toward Dr. Sara...... and the radio goes silent. He is astonished to learn he could actually kill someone who is not even near him. Streator later does the same thing to the two men who are eulogizing Dr. Sara over the radio.