06/12/2007 AT 05:50 PM EDT
Monday night was ladies' night for Britney Spears
, who hit the town in L.A. with her assistant and BFF, Alli Sims, and some female friends.
For dinner it was SHU Sushi House Unico in Bel Air, which has become a favorite haunt of the singer's. As always, she and her group dined in a private upstairs area, says a source, adding that Spears enjoyed her usual: California roll and a salad.
"She seemed happy," says the source. "She just enjoyed the music [an XM "Chill" station], the atmosphere and the food. She was just having
Next the pals hit Guy's, followed by a brief stop-off at Winston's. "Britney and Alli were holding hands, not leaving one another's side," says a clubgoer. "Britney spent much of her time whispering into Alli's ear, smiling, drinking a bottle of water – [she seemed to be] in a really good mood, goofing around."
Just before 1 a.m., Spears and friends arrived at the hip Hollywood hangout Joseph's, but by then, the evening was winding down. "Britney was pretty subdued," says a witness. "She didn't really appear to be having a good time. She was casually talking with Alli. All the guests were swarming around her table to try and get a peek."
With reporting by ALEXIS CHIU