Samantha Ronson was arrested at 10.30 on Monday morning for driving under the influence.
Lindsay Lohan's ex-girlfriend is said to have been driving home when she was stopped by police for speeding in LA.
Samantha - Mark Ronson's sister - was travelling back from Las Vegas where she had performed a DJ set on Sunday night.
According to reports, she was given a field sobriety test but didn't perform well.
Samantha later reportedly refused to submit to a breathalyzer and was arrested on the scene.
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