Radar Online released the clip Tuesday. making it clear why the troubled socialite lost custody of her and Sheen's twin boys back in May.
The clip shows the 36-year-old former reality TV personality smoking from a glass pipe -- common for crack users -- while haggling with a man for crystal meth.
"Where's the crystal?" Mueller asks in the video. "I'm giving you $1,500."
According to Radar, the man behind the camera released the footage in hopes of helping Mueller stay clean and complete her current rehabilitation program.
"Brooke loved getting high," the source said. "This was just another crazy night of her getting high. When she did drugs, it was three to four times a week. I know that she is aware that if she doesn't stop doing drugs, she is going to lose her kids (for good)… hopefully she can stop."
Mueller is a Palm Beach, Fla. socialite who previously worked as a special correspondent on "Extra," a reality TV personality on "The World According to Paris" and various acting gigs.
The Los Angeles County Department of Children and Family removed Mueller's twin boys, Bob and Max, from her custody on May 3. Temporary custody was given to Sheen's ex-wife, Denise Richards.