Who is Stephanie from Valis and what is their importance?

Stephanie is an 18-year-old drug dealer living and working in Horselover Fat's neighborhood in Santa Ana, CA, Stephanie is a major factor in preventing Fat's death as he mourns the suicide of his friend, Gloria Knudson. Stephanie lives for hashish, which she consumes and peddles, along with marijuana and sometimes cocaine. She refuses to sell hallucinogenics like LSD (acid).