03/31/2008 at 04:30 PM EDT
was hospitalized in Los Angeles for a kidney infection, her rep tells PEOPLE.
The singer "has been released and is doing fine," the rep says.
Simpson, 27, went to Cedars-Sinai Medical Center on Friday after suffering a fever.
Earlier this month, Simpson took a trip to Iraq
where she performed for the troops. She is currently working on a country album.
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