On Saturday, Christina stood in line with a neighbor, eager to meet Giffords in front of a neighborhood Safeway about 10 a.m.
Moments later, a crazed gunman shot Giffords in the head with a semiautomatic weapon and then sprayed the crowd, killing U.S. District Judge John M. Roll; Giffords' aide Gabe Zimmerman, 30; Dorothy Morris, 76; Dorwin Stoddard, 76; and Phyllis Schneck, 79.
Christina, the bright-eyed, vivacious girl who was born in West Grove, Chester County, died from a bullet that struck her in the chest.
"I think it's horrible," said Tucson neighbor Jean Perry, 75, adding that she would often see Christina traveling to and from school. "Before I knew it was my neighbor, I thought it was tragic that a young child was killed. Then I found out it was my neighbor."
Jared Lee Loughner, 22, is in custody and has been charged, but it is not clear what exactly inspired his deadly rampage.
Friends reportedly described Loughner as a pot-smoking loner whom the Army rejected when he tried to join in 2008. Last year, he dropped out of a local community college after five encounters with campus police for classroom and library disruptions. Pima County Sheriff Clarence Dupnik reportedly described Loughner as mentally unstable.
According to FBI Director Robert Mueller, Loughner attended a similar congressional meet-and-greet event for Giffords three years ago. In one of several YouTube videos, Loughner spoke about inventing a new U.S. currency and complained about the illiteracy rate in Giffords' congressional district.
In addition to the six killed, 14 people were injured by the time two people tackled Loughner and another tried to pull a clip away from him before he could reload, but the damage had already been done.
Giffords, 40, has undergone surgery at the University Medical Center in Tucson, and doctors are optimistic about her chances of survival after a bullet passed through the left side of her brain.
As for Christina, she will forever be remembered as a promising girl gone too soon.
"From the very beginning, she was an amazing child," her mother, Roxanna Green, told the New York Times. "She was very bright, very mature, off the charts. She was the brightest thing that happened that day."
Roxanna, a registered nurse by training, was a stay-at-home mom. Grandfather Dallas Green was a former Phillies pitcher and the field skipper for the team when they won the World Series in 1980; he still works for the team.
When Amaro spoke to him, Green and his wife, Sylvia, a former Delaware schoolteacher, were en route to Arizona from their offseason residence in the Islands of Turks and Caicos, in the Caribbean.
Naturally, baseball ran through Christina's blood. She was the only girl, a second baseman, on the Canyon Del Oro Little League baseball team, dubbed the Pirates.
Christina reportedly loved animals and was a passionate dancer with a thing for ballet, hip-hop, jazz and gymnastics. She was an athletic girl who enjoyed swimming with her 11-year-old brother, also named Dallas.
Christina enjoyed singing in a church choir at St. Odilia's Catholic Church, where she received her first Holy Communion in the spring, according to news accounts.
Even at her tender age, according to local news accounts and the Times, Christina was a concerned citizen who aspired to influence change. She reportedly belonged to a charity called Kids Helping Kids, and she tried to help children less fortunate.
Christina was born in the midst of chaos - the day terrorists killed nearly 3,000 people. Roxanne told the Times: "It was an emotional time for everyone in the family, but Christina's birth was a happy event and made the day bittersweet."
The Associated Press contributed to this report.
