The attack happened Oct. 22 on the back porch of the family's home about six miles outside of Rocky Mount.
The mother of the child said she tried to stab the dog to get it off her baby.
"This animal was strong and she did try to stab it, beat it, and get him off and it did not work," said Edgecombe County Sheriff Cleveland "Clee" Atkinson Jr.
When an Edgecombe County sheriff's deputy arrived, he said the child was in the dog's mouth and being slung around.
"They described it as the pit bull shaking a doll baby," Atkinson said. "That's how aggressive it was."
The deputy shot and killed the dog. It took two shots to take down the pit bull mix.
"Officer Whitaker shot the dog twice with his service weapon," Atkinson said. "He's definitely a hero and he saved that baby's life."
The child was taken to a nearby hospital and then flown to Vidant Medical Center in Greenville for treatment.
The child remains in the hospital receiving treatment for her injuries.
The Edgecombe County Sheriff's Office will not release any names out of respect for the family.
"We ask that everyone keep the little girl and her family in their thoughts and prayers," Atkinson said. "We hope for a full recovery for the little girl. No charges are expected in this matter."
The child is now at UNC Hospital in Chapel Hill and is listed in very serious but stable condition.