An underdog story if ever there was one: A puppy from an abandoned hotel in middle-of-nowhere South Carolina, picked up by an all-kill shelter where owners have 48-hours to claim a dog before it is euthanized. With only hours left, this dog's fate is changed by a woman many kilometres away.

Rescue groups brought the dog to Christy Wrede in New Jersey, who saw something in her and began agility training immediately. And three years later, through hard work and a good dose of luck, Emma was chosen to compete this week at the biggest dog show in the world, the Westminster Kennel Club's annual event in New York.

"Would you ever think it possible? From death row to Westminster?" Ms. Wrede said, like a proud mother. "This dog has come from Redneckville to New York City. The chain of events has just been amazing."

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Ms. Wrede saw Emma's photo in an e-mail from the rescue group she volunteers with and decided to take her.

"There was something extra special, some intangible thing," Ms. Wrede said from her home, her voice cracking.

Ms. Wrede, a special-needs teacher, has no professional dog training background, but took it up as a passion, training Emma in agility, and another rescue dog, Logan, who had been deemed dangerous.

"There's no such thing as a dog who wants to misbehave. A lot of agility training comes down to common sense – understanding dogs like treats, and need patience."

Westminster has been traditionally a stage solely owned by purebreds duking it out for Best in Show – this year's winner will be chosen on Tuesday evening. But for the first time, the show added an agility contest, inviting mixed-breeds – "all-American dogs," in show-speak – to strut their stuff.

Emma, who according to a DNA test, is "half Boston, quarter boxer, and a quarter mumble jumble of who knows what," Ms. Wrede said, was one of 15 mixed-breed dogs out of 225 chosen in a draw to compete.

Long regarded as a forum for well-groomed, pampered purebreds, Westminster's invitation to mixed breeds in agility is a welcome addition for David Frei, long-time host of the show.

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"We like to say it's a celebration of all dogs – and this brings new, excited dogs, attacking the course, running through tunnels, jumping through tires, weaving through poles, across teeter totters – dogs being dogs."

He said the exclusion of mixed breeds in the past was not snobbery: "It's impossible to judge a mixed breed in a Best of Show contest … judged against a set standard of what their breed should be.

"But mixed breeds have every trait you can imagine, coats of all kinds, ears pointing every which way, and, so often, a special attitude about life."

He stresses that all dogs at Westminster are family dogs. "They don't sit around on doggie cushions eating doggie bonbons. They're stealing hot dogs, drooling everywhere, drinking water out of the toilet – just like your dog at home."

For Ms. Wrede and her Emma, the little dog that could, the invitation to the biggest, most prestigious dog show in the world sends a big message.

"You don't have to spend thousands of dollars on a dog for it to surpass your wildest dreams."