Bynes, 27, requested she be released from the hospital Thursday, but a judge extended her stay so she can be properly evaluated and treated, the celebrity news website said.
The former "What I Like About You" star's parents, Rick and Lynn, are expected to appear in court Friday to seek conservatorship of Bynes because they feel she is a danger to herself and others.
Bynes allegedly caused a disturbance when she tried to break into a retirement community in her hometown of Thousand Oaks, Calif., last Sunday.
The following night, she reportedly set a small fire in someone's driveway, which led to police involvement and her eventual hospitalization.
"Deputies investigated the incident and determined that she met the criteria of 5150 W&I [California Welfare & Institutions Code]. She was detained and taken for a mental health evaluation," Capt. Don Aguilar of the Ventura County Sheriff's Office told Hollyscoop Tuesday.
The actress is known for her work on "The Amanda Show," as well as in the films "Hairspray" and "What a Girl Wants," but her last major screen credit was a supporting role in 2010's "Easy A."
Her once-bright career has been eclipsed in recent years by her bizarre Twitter rants and frequent brushes with the law.