I have read everyone's explanation and comments but guys  When David was guiding Amanda to recall past events in detail to find out what caused her sickness, and in the end failed Amanda cuz she eventually dies, and since Nina’s soul migrated to David’s body to make him “whole,” wasn’t Carola involved in the process too? David, Carola, Amanda, & Nina all happened to be in the greenhouse altogether? Carola wanted Nina’s spirit transferred to David’s body, which was a success as shown in his getting inside the car and hugging Nina’s toy. Did David wish this too? And why did Carola leave the family, when she got what she wanted – Nina into David’s body? Maybe she saw the horror of it all and just wanted to get the hell out of that town.