Who is Sherri Solvig from Valis and what is their importance?

Sherri Solvig is a friend of Horselover Fat's. She is suffers from lymphatic cancer, and over the course of the novel, loses her life to the disease. Before going into remission, Sherri suffers terribly from chemotherapy, becoming nearly blind and deaf, and experiencing constant seizures. She continues to believe, however, that God is healing her. She intends to enter a religious order when she is cured.