Christina, one of six who died in Saturday's shooting, had been featured in the book "Faces of Hope, Babies Born on 9/11," about children born on the day of the worst terrorist attack in U.S. history.
"She came in on a tragedy and now she's gone out on a tragedy, but the nine years in between were very special," her father, John Green, told CNN. "We're all going to miss Christina. We were four people, and now we're three."
According to The Arizona Republic, a neighbor invited Christina to go along to the "Congress on Your Corner" event at a Safeway supermarket because he thought the newly elected student council member and aspiring politician would enjoy it.
"The next thing you know, this happened," said her uncle Greg Segalini. "How do you prepare for something like this? My little niece got killed -- took one on the chest and she is dead."
Christina, who loved ballet, was the granddaughter of Dallas Green, former manager of the Phillies, Yankees and Mets. Her father is a scout for the Los Angeles Dodgers organization.
"We lost a member of the Dodgers family today," owner Frank McCourt said in a statement. "The entire Dodgers organization is mourning the death of John's daughter Christina and will do everything we can to support John, his wife Roxanna and their son Dallas in the aftermath of this senseless tragedy."