Deviating from his prepared script, the president then ignited a crowd of 13,000: "I want America to be as good as she imagined it."
Led by law enforcement officials in white gloves, pallbearers wheeled Christina's casket into the church. Her parents, John and Roxanna Green, and her brother, 11-year-old Dallas, followed, holding hands and bowing their heads.
The entry to the church was framed by a 30-foot-wide flag known as the National 9/11 Flag, which flew atop the south tower of the World Trade Center the day it fell. Shredded and lifted from the wreckage, it was largely forgotten until 2008, when a foundation brought it to Kansas, where volunteers — many of whom had survived a series of tornadoes — used flags found in tornado rubble to patch it up.
The flag will soon become part of the permanent memorial museum on the former site of the World Trade Center. Several mourners noted Christina's connection with baseball; her father is a Dodgers scout and her grandfather Dallas Green managed the Philadelphia Phillies to a World Series victory in 1980.
A remembrance posted Thursday on the website of Christina's baseball league noted that she could frequently be found between innings singing pop songs with the right fielder.
She was not, however, a token girl. Last season, after she'd fouled off several pitches, she was plunked hard with a fastball. The rules allowed her to either go to first base or continue her at-bat. Christina replied, "I want to hit."
Her father told the crowd that he would miss "coming from two weeks on the road off baseball, walking in the door and hearing music and seeing my wife and daughter dressed to the nines dancing around the house."
Hundreds of people who had lined the funeral procession remained outside for the duration of the service.
"That's Tucson for you," said Mike Oravetz, a mail carrier who moved from Long Beach to Tucson in 2006. "Tucson takes care of its own."
Pamela Keyes' children, 4-year-old Zia and 6-year-old Zachary, had been brimming with questions since the attack, especially about Christina. For answers, she dressed them in white and brought them to the funeral.
"We've talked a lot about good guys and bad guys, the goodness in people, and what happens when someone dies," Keyes, 48, said. "Tucson really needs goodwill right now."
Also Thursday, the Pima County Sheriff's Department revealed that a man walking his dog near Loughner's house discovered a black bag abandoned in a desert wash. The bag contained 9-millimeter ammunition, the same kind of bullets used in the shooting, and officials said they believed it belonged to Loughner. The FBI was conducting further analysis.
Authorities had said that Loughner and his father, Randy Loughner, got into a brief dispute the morning of the shooting when the father caught the son removing a black bag from a family vehicle.
NASA, meanwhile, said it had chosen a backup commander for an April space shuttle mission, the one that Kelly, Giffords' astronaut husband, had been scheduled to command.
Kelly remains on the books as the mission commander, NASA said, but astronaut Rick Sturckow has been named backup commander to take over in the event that Kelly is forced to drop out, though Kelly said in a statement that he remained "very hopeful" to rejoin his crew in time.
Hours after the funeral, First Lady Michelle Obama released a letter to the nation's parents. She said many children, including her own daughters, had begun asking difficult questions since the attack.
They "don't lend themselves to easy answers," she wrote. "But they will provide an opportunity for us as parents to teach some valuable lessons — about the character of our country, about the values we hold dear, and about finding hope at a time when it seems far away. We can teach our children that here in America, we embrace each other, and support each other, in times of crisis."
She said parents could respond by teaching the values of tolerance and community service, and by reminding them of the importance of the lives lost that day, including Christina's.
Mehta reported from Tucson and Gold from Los Angeles. Times staff writer Rong-Gong Lin II in Los Angeles contributed to this report.