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Patients at the Betty Ford Center typically earn privileges to go off campus for occasional shopping or a meal – but Lindsay Lohan
won't be one of them.
Lohan, who's serving a 90-day sentence
at the Rancho Mirage, Calif., facility for violating probation
, will be confined to the sprawling desert grounds, according to a letter addressed to Lohan's attorney Shawn Holley and filed with the L.A. Superior Court.
"It is understood by the Betty Ford Center that your client is to remain on the premises for the duration of her 90-day stay in treatment," the document reads.
But the facility is a far cry from a lock-down penitentiary.
"We can't hold a patient against their will, we can't stop a patient from running away. We're not a jail," an intake counselor previously explained to PEOPLE. "But we closely monitor patients via security and technicians 24 hours a day."
Patients are forbidden from having a cell phone, can only make brief calls or use the Internet on weekends, and are drug tested randomly.
The letter adds that Lohan will be treated by a battery of experts, including a physician, nurse, psychologist, case manager, spiritual care counselor, family counselor, dietician, fitness trainer and a chemical dependency technician in a strict hour-by-hour schedule, usually starting at 6 a.m. and ending at 9 p.m.
"There is physical exercise and group therapy everyday," the counselor explained. "This is not a vacation."
Lohan's previous stay at Betty Ford included a scuffle with an employee
in Dec. 2010 that involved police, but local prosecutors stated there wasn't enough evidence for a case.