Tucson, Arizona (CNN) -- When President Barack Obama said Wednesday night that Rep. Gabrielle Giffords had opened her eyes for the first time since being shot on Saturday, an overflow crowd of nearly 30,000 people at a memorial event erupted into cheers that the congresswoman may have heard in her hospital room.

Obama said he learned of the eye-opening from Giffords' husband, astronaut Mark Kelly.

"She knows we're here, and she knows we love her,and she knows that we will be rooting for her throughout what will be a difficult journey," the president said at a memorial in Tucson to honor the victims of the shooting.

Giffords is still listed in critical condition at the University of Arizona's University Medical Center. Suspect Jared Loughner allegedly fired at her first, striking her in the head.

As soon as Obama finished his remarks, Sen. Kirsten Gillibrand, D-New York, let it be known that she, Rep. Debbie Wasserman Schultz, D-Florida, and House Minority Leader Nancy Pelosi, D-California, were in the room at the time, along with Kelly and Giffords' parents.

"It was like witnessing a miracle," Gillibrand told CNN.

"Debbie and I were telling her how much she was inspiring the nation with her courage, her strength, and we were talking about the things we wanted to do as soon as she was better," the senator said.

"I said, 'We'll have another night out for beer and pizza with your husband.' And Debbie started talking to her about their house in New Hampshire, just talking about all the things we wanted to do, and all of a sudden she started to struggle to open her eyes. So Mark saw that and said, 'Open your eyes, Gabby, open your eyes.' She kept struggling and struggling and Mark just kept encouraging her. And within a moment she literally opened her eyes."

"The doctors couldn't believe it," Wasserman Schultz said.

"Mark started encouraging her, saying 'Gabby, give me a thumbs up if you can see, if you can see me, touch my ring, touch my wedding ring.' She started doing that," she said.

"We just kept talking to her and talking to her about the fun we've had with her, and so then she opened her eyes more. She went from opening her eyes really just in slits to opening them nearly fully. It wasn't very long, and then they closed again. But it was just absolutely -- it was the most incredible, aside from my kids, the most incredible experience."

Giffords kept her eyes open "for a moment," Gillibrand said -- "maybe 30 seconds, maybe 60 seconds."

"You could see she was focusing and Mark said, 'Gabby if you can see me, give me the thumbs up,' and not only did she give the thumbs up, she literally raised her entire hand," Gillibrand later told CNN.

Doctors sent them out of the room shortly after that, Gillibrand said, because Giffords needed to rest.