Paige Barenskie underwent surgery to repair damage to her nose and cheek after the Staffordshire bull terrier-cross attacked her in 38th Avenue, north Hull, last Wednesday.
Mark "Harry" Falkingham, 34, who owned the dog, named Buster, for 18 months, says he took him to pet charity, the PDSA, where the animal was destroyed.
He said: "I feel really sorry for Paige. It should not have happened.
"I had no choice but to put Buster down. He had never bitten anyone before, but once they bite someone, you can never trust them again – you have to put them down. Any responsible dog-owner would have done the same in my position."
Paige's mum, Gemma Barenskie, was present when the dog attacked as her daughter played with other children in her neighbour's front garden.
Mr Falkingham, who lives two doors away from Mrs Barenskie, said the dog had crawled through a gap in a fence and into next-door's garden, where it lunged at Paige.
Paige's three-year-old brother, Hayden, was among several people who witnessed the attack.
Mr Falkingham shed more light on the three-year-old dog's past.
He said: "I got Buster from a friend who moved out of the area. He read about the attack in the Mail and was pretty upset. Buster had grown up around kids. He has a kid about Paige's age. He has an older one as well. Buster never attacked either of them.
"We have no idea why he attacked Paige, but she did not do anything wrong."
Her aunt, Kira Adamson, said although scarred, she is making a good recovery at home after spending a night at Hull Royal Infirmary.
She said: "Paige is getting back to her normal self. She is in a bit of pain – her cheek hurts the most – but she's getting better."
Miss Adamson said the family is satisfied with the way the dog's owner has dealt with the situation.
She said: "I knew Buster since Harry got him. "He was a lovely dog, but Harry has done the responsible thing and had it put down after what happened."
Miss Adamson said her niece was sent home from hospital with antibiotics and cream to apply to her wounds.
She said: "Paige has to go back to see her consultant in six weeks' time. We will know more then. It's possible she will have plastic surgery."
A Humberside Police spokesman said officers were not intending to take any action against the owner.
(This is Hull and East Riding - July 29, 2013)
