After serving 13 full days in a solitary cell, Lindsay Lohan was freed from a Lynwood, Calif., jail in the wee hours of Monday morning.

"She was released at 1:35 a.m.," Los Angeles Sheriff's spokesman Steve Whitmore said outside the jail. "She has been sent directly to her next destination, which is a treatment center. And she will now be under the supervision of the L.A. County probation department. This concludes her custody."

The actress had been serving a 90-day sentence for violating probation in a DUI case, but served a reduced sentence for good behavior and due to the sheriff's long-standing policy of releasing nonviolent offenders early because of severe overcrowding.

Lohan was expecting to serve her court-ordered three months in rehab at an Orange County, Calif., facility, but the judge in her case changed her mind last minute over the weekend.

"There was concern that [Morningside Recovery] was not a secure enough facility," District Attorney spokeswoman Jane Robison told PEOPLE. Robison added that Judge Marsha Revel was concerned that drugs could be easily passed onto the actress, and therefore approved of an undisclosed L.A.-area rehab center. The facility is at UCLA Medical Center.

If Lohan violates any rules during her treatment, the court could be notified and the judge could potentially throw her back in jail for violating probation, legal experts say.

She also faces a year of random drug testing. The actress must stay clean and sober until August 2011, when her probation term is over. She is, however, allowed to take a number of prescription medications.