01/18/2007 at 03:00 PM EST
Britney Spears may have spent one wild weekend in Las Vegas
with new beau Isaac Cohen, but come Wednesday night, she was back to work.
After a half-hour break to fuel up
with pals at the Hollywood eatery Hamburger Mary's, the singer, 25, was spotted at 10:30 p.m. at the nearby Record Plant recording studio.
"She was rehearsing material, working hard and having fun all at the same time," a witness tells PEOPLE.
As for the project at hand, Spears herself told fans earlier this month in a message on her Web site
, "I've been working so hard on this new album and I can't wait for you all to hear it and to go on tour again! I would like to exclusively tell you that I am working hard to release the new album sometime later this year, but the date is of course not certain yet."
She added, "I look forward to coming back this year bigger and better than ever, and to also reaching out to my fans on a more personal level."
Her manager, Larry Rudolph, told USA Today
that Spears was about half-finished with the new disc. "She's real excited," he said, estimating that the single would be out by late summer with the album to follow in late fall.