Dr. Peter Rhee of University Medical Center told KVOA-TV, Tucson, Giffords' feat is the result of "aggressive rehab" and said she also was able to sit in a chair in her hospital room and look at the Catalina Mountains.
Giffords' mother, Gloria Giffords, said Tuesday the congresswoman will be moved Friday from UMC to a rehabilitation facility in Houston. Hospital spokeswoman Darci Slaten declined to confirm the transfer date.
In an e-mail message to family friends obtained by CNN, Gloria Giffords wrote: "There is a team of medical specialists involved ... including military surgeons who specialize in bullet wounds to the head. They want to start aggressive rehab immediately."
Gloria Giffords wrote her daughter is improving every day "and shows higher levels of comprehension and complex actions."
When Gabrielle Giffords' husband, Mark Kelly, returned to the hospital after speaking at her aide's memorial service, she "untied his tie and undid the top button to his shirt," her mother wrote.
Gloria Giffords said Kelly gave his wife cards from schoolchildren and a large-print Harry Potter book to read, and Gabrielle Giffords gave him "a 20-minute neck and back rub."
Gabrielle Giffords remains in serious condition.
Kelly said she will recover and probably return to the supermarket where she was shot.
"I can almost guarantee you what her first event will be," he told the Tucson Sentinel. "I'd be shocked if the first thing she does is not 'Congress on Your Corner' at that Safeway."