How was Dr. Neal Townsend an important person in Natalie's life in the novel, When I’m Gone?

Dr. Neal is mentioned throughout the novel by Luke, not understanding his connection to Natalie. We do not meet him until the last few chapters finding out that he had adopted Luke and Natalie’s daughter after Natalie gets pregnant at 15. Dr. Neal had supported Natalie when she went back to college and helped her deal with her cancer diagnosis.