The police blanketed the 23-year-old woman and asked her questions to determine her state of mind.
Joe Mendoza says Marquez was having a seizure when South Pasadena officers arrived, and paramedics treated her.
Friend Terence Towles Canote says the actress was having health and financial problems but was hopeful about a career comeback.
Police were called when neighbors reported a woman having sex with her pit bull in her backyard in broad daylight.
The dog meanwhile was taken into the custody of Animal Control.
The Los Angeles Sheriff's Department said Friday that 49-year-old Vanessa Marquez died at a hospital following the shooting at her South Pasadena apartment Thursday.