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

Sherri Solvig is a friend of Horselover Fat's, Sherri is dying (and ultimately dies) of lymphatic cancer. Before she goes into remission, Sherri suffers terribly from chemotherapy, becoming nearly blind and deaf, and experiencing constant seizures. Still, she believes that God is healing her. Sherri intends to enter a religious order when she is cured and is in everything a fervid Christian except in showing any practical Christian charity.