09/19/2007 at 02:15 PM EDT
After a judge ordered random drug tests for Britney Spears
, the singer hit the Los Angeles nightclub scene overnight Tuesday with Avril Lavigne
Followed by a pack of paparazzi, Spears first was seen at Winston's in West Hollywood with Lavigne and Spears's friend Alli Sims.
The women left around 1 a.m., and Spears was later spotted at Hyde Lounge in West Hollywood until the club closed.
"They kept bringing (Spears) shots and so they were drinking," says a Hyde observer. "She was dancing on the tables trying to be really sexy, even putting a black sock over her head as a hat, and putting on a show for everyone."
Another observer saw what appeared to be alcohol in front of Spears but didn’t see her drink it.
At one point in the evening, Spears drove to the Beverly Hills Police Department and complained that photographers were following her, but no action was taken.
Spears's partying came after the judge in her custody fight with Kevin Federline
found that she is a "habitual, frequent and continuous" user of alcohol and controlled substances
, and now must submit to random twice-weekly testing.
Los Angeles Superior Court Commissioner Scott Gordon also ruled that both Spears and Federline may not consume alcohol or non-prescription controlled substances at least 12 hours prior to being with their children.
Reporting by MARY MARGARET and KEN LEEWho's turning 40? Which celebs are high school dropouts? What's hot and definitely not in fall fashion?
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