Some of the organs went to a little girl in Boston, CNN reported.
"It was very poignant to find out. That's what Christina was all about," father John Green told CNN. "It's a blessing."
The girl, known for her giving spirit, went with a neighbor to the Giffords event at a Safeway store last Saturday because she was recently elected to her student council and had a budding interest in politics.
The organ donation was first disclosed by the bishop of Tucson, the Most Rev. Gerald Kicanas, speaking at Christina's funeral Thursday. A friend helping the Green family told the Arizona Republic that the organ donation network called the family on Friday, telling them that Christina's donation had already saved the life of a child on the East Coast.
Asked if he would like to meet the girl who received the transplant, John Green told CNN, "Oh yes, and I'd give her a big hug."
Christina was fatally shot when a man opened fire at the event in Tucson. Jared Lee Loughner, 22, is facing federal charges in the attack, which killed six people.
Mourners at Christina's funeral entered beneath the National 9/11 Flag, a massive patchwork of fabric rescued from the Twin Towers. A New York firefighter brought the flag to Tucson to honor Christina, according to the Arizona Republic.
"I can't tell you how much we all miss you," her father said during the service.
"I think you have affected the whole country."