Lindsay Lohan might be teetering her way back toward sobriety -- but her ex-girlfriend, Samantha Ronson, is apparently off the wagon. reports that Ronson was arrested for DUI on Monday, following a deejaying gig at Lavo nightclub in Las Vegas.

Ronson, 33, was pulled over for speeding in her black Porsche outside of Baker, Calif. at approximately 10:30 a.m.

After performing poorly on a field-sobriety test and refusing a Breathalyzer test, Ronson was hauled into the Baker Sheriff's Department substation, where a test determined that her blood-alcohol level was over the legal limit.

Ronson, who was reportedly cooperative during the arrest, was released later in the day.