updated 03/07/2014 AT 12:00 PM ET
•originally published 03/07/2014 AT 6:25 AM ET
On Thursday, she posted a photo on her recently renamed Twitter account of a redheaded lady – which, judging by the wrist tattoo, is the singer herself – looking out of a plane window.
“Happy to be back! Feeling healthy & working on tons of new music,” she wrote. “I can’t thank my fans enough for all the love & support u have given me.”
After posting some emoji hearts and a rainbow, she added: “life is beautiful. I’m so blessed to have u all.”
Her return came as a surprise even to those close to her. One pal says they “really had no timeline” for her treatment. “I had no idea she would be out today,” the pal added.
Last month, the the singer postponed her spring concerts to focus on getting “her health back on track,” she said in a statement.
As PEOPLE reported exclusively, the singer’s mom, Pebe Sebert, also entered into the same Chicago-area rehab center as her daughter.
“Ke$ha wants me to heal along with her,” Sebert told PEOPLE at the time.
With reporting by PATRICK GOMEZ