Lindsay Lohan checked back into rehab this week.The 'Mean Girls' star - who was arrested for Driving Under the Influence(DUI) on Saturday - checked into Malibu's Promises center,where Britney Spears was recently treated. A source told In Touch Weekly magazine: "She realises it's the right thing to do. She is going willingly."Lindsay, 20, was due to check in to the center yesterday afternoon. But witnesses claim they saw the actress "partying hard" at a 944 Magazine party at Hollywood's Teddy's nightclub on Sunday night. Insiders say Lindsay insisted she didn't care about the consequences of her arrest after alleged cocaine was found in her car after Saturday's crash.She was photographed later that night looking dishevelled, passed out and worse for wear in the front passenger seat of a car being driven by her DJ friend Samantha Ronson.Lindsay was driving her black Mercedes convertible on Saturday when she clipped the curb and hit bushes on Sunset Boulevard at 5.30am. Los Angeles Police Lieutenant Mitch McCann - who is heading the investigation - said the actress was not seriously injured but was taken to Century City Doctors Hospital for treatment for minor chest injuries. McCann also revealed a "usable amount" of cocaine was recovered from the severely damaged vehicle during the investigation.The 'Just My Luck' star - who had been partying at Les Deux nightclub before moving on to a private bash and then the Skybar at the Mondrian hotel - was charged with DUI at the hospital, and McCann said "additional charges may be filed."Lindsay completed a 30-day course at Los Angeles' Wonderland rehab facility checking in on February 16, and also attended Alcoholics Anonymous meetings.However, since leaving the facility the 'Georgia Rule' actress has been accused of secretly drinking vodka from a water bottle when out partying.Meanwhile, Lindsay's father has insisted she and her mother Dina should go to rehab.Michael - who has be estranged from Lindsay since he was jailed for DUI and assault charges in 2005 - said: "The people out there in Hollywood with her are in it for the money. They want to see what they can get. She needs to go to rehab and my ex-wife Dina should go with her."The writing was on the wall years ago. She needs a faith-based program."