Dina Lohan confirmed to E! that her daughter has left rehab, calling it "a great day."
Lindsay Lohan made a hopeful post on Twitter, writing, "Today is the first day of the rest of my life."
She then quoted Mahatma Gandhi, posting, "The future depends on what we do in the present."
Judge Elden Fox sentenced Lohan, the "Mean Girls" star, to her latest stint in rehab in October after she failed a drug test.
Dr. Mitch Rosenthal, a psychologist and the founder of Phoenix House, a substance abuse service organization, said Lohan must make her recovery paramount.
"She's got to surround herself with sober friends and work very hard at maintaining sobriety. It isn't a part-time thing," Rosenthal said. "It is really saying, 'I have a very serious illness and I have to work at it the way I have to work at hypertension and diabetes, I have to manage this illness.'"
As a child-actress who grew up on screen and in the public eye, Lohan saw the Hollywood nightlife begin to take a toll on her in 2007.
She was arrested twice. She served three jail sentences and five rehab stints. She pleaded guilty in August 2007 to two misdemeanor counts of being under the influence of cocaine, no contest to two counts of driving with a blood-alcohol level above 0.08 percent and one count of reckless driving.
The first time Lohan was sent to prison she broke down, sobbing in the courtroom. After being released, her ankle bracelet monitor revealed that she had slipped again.
Lohan poked fun of herself at the MTV Video Music Awards in September, telling host Chelsea Handler, "Don't you know nobody wants to work with a drunk, take it from me ... get a hold of yourself."
Her latest stint in rehab had been relatively quiet until last month when police were called to the Betty Ford Center early Dec. 12 after a staffer accused Lohan of battery.
"On Dec. 12, 2010 at 1:03 a.m. officers from the Palm Desert Police Department conducted a battery investigation," the statement said. "The incident involved Lindsay Lohan and another female adult who is a staff member. Lohan was reported as a suspect in the investigation. The victim desired prosecution."
The staff member was fired but Lohan remains under investigation.
Lohan, Dad Can Help One Another
Rosenthal said Lohan's sobriety will depend, in part, on with whom she surrounds herself.
"She's got to be surrounded with sober people," he said. "She's got to stay out of places that give her cues for drug use and drinking. She should not be in bars. She should not be at friend's homes where liquor is being used or marijuana is being used."
Rosenthal said rehab might have given Lohan clarity on her relationship with her father.
"It would be great if they [Michael and Lindsay] worked on it [sobriety] together and it would be great if he is a healthy influence on her life. She's going to have to decide that," Rosenthal said.
As those around her hope that she keeps her personal life together, Lohan has already launched her professional comeback with a sizzling photo shoot. In the pictures, Lohan poses in front of a background of jumbled words.
Still, the actress hasn't headlined a movie in more than three years.
She was back in rehab when "Machete," her most recent film, was released. She played a pistol-packing nun.
Her legal troubles and addiction problems cost her a part playing the real-life story of porn star Linda Lovelace.
Howard Bragman of 15 Minutes PR said Lohan shouldn't rush to headline a film.
"If she's smart, she won't be expected to carry a project," he said. "She'll get a juicy role in a smaller movie, one that will showcase her talents because she's got the chops."
Lohan can rebuild her career by staying quiet and taking smaller roles, Bragman said.
"A lot of what she has to do is very counterintuitive," he said. "A lot of celebrities say I got where I was by being charming, by talking, by tweeting. I'd like to see her be quiet. I'd like to see her work speak for herself."
Bragman said the comeback of Britney Spears should be a model for Lohan. Spears took bit parts on sitcoms and focused on her music in the wake of her breakdown.
"All we've hear about Britney is her work, her concerts and her music and that's what we'd like to hear about Lindsay," Bragman said.
Despite struggles with addiction, Lohan has remarkable talent, Bragman said.
"This girl is only 24, that's what's so sad about this," Bragman said. "The Hollywood community really wants this kid to get back on her feet."
For now, Lohan will have to submit to random drug tests as a condition of her release. She also needs to satisfy a criminal judge that she has been in compliance with her probation terms during her three-month stint at the Betty Ford Center.
ABC News' Sheila Marikar and the Associated Press contributed to this report.