Shortly before her first birthday, Harriet Ringsell was diagnosed with cerebral palsy - a motor impairment caused by brain damage that prevents its many sufferers from walking due to sometimes painful muscle spasms.
"She seemed perfectly healthy at first," recalls her mother Sue. "But by 11 months, we noticed that Harriet couldn't sit up on her own and seemed to find it hard to move."
Blood tests and MRI scans confirmed it was cerebral palsy.
"We were distraught but after the initial shock we knew we just had to get on with it," says Sue, 44.
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Devoted: Harriet with Yeppa, a wire-haired Vizsla who is helping her battle to be mobile
Harriet, an only child and now 11, spent most of her childhood in a wheelchair - until Yeppa, a Hungarian wire-haired Vizsla, arrived.
Remarkably the dog, which Harriet lovingly describes as "her best friend", has enabled her to walk.
"I can get about without my wheelchair now," she says enthusiastically from the garden of the cottage where she lives with her mother, a hairdresser, and father Adrian, 46, who owns a cleaning firm, in Hawridge, a quiet Buckinghamshire village.
"I can even walk on my own for short distances without my special walking frame. It's all thanks to Yeppa."
And now, because of her trusted companion, Harriet is about to undergo an operation that it is hoped will help her to walk completely independently.
It was in recognition of the incredible assistance Yeppa gives Harriet that she and her beloved pet won the Friends For Life award at this year's Crufts.
Five finalists were selected from 12,000 nominations and Harriet and Yeppa were chosen by public vote, based on which dog had helped its owner most significantly.
"I was nervous but getting the award was exciting," says Harriet. "I was really happy but overwhelmed and that's why I was in tears.
"Yeppa got up on my lap to protect me when I started crying." Scroll down for more...
Faithful: Yeppa joins her in the pool for regular swim therapy
Yeppa arrived when Harriet was eight. Adrian carried her when they went to select their new family pet and as soon as he sat Harriet down, Yeppa snuggled up in her lap.
"The difference the dog has made to life is immeasurable," says Sue.
"Harriet saw other children walking and running and tried to join in but most days she was restricted to her wheelchair.
"Once, after seeing some of her friends running, she said to me, 'I just want to know how it feels.'
"After we'd had Yeppa for a couple of days, Harriet tried to walk using her frame. We watched in amazement as Yeppa gently took one of her hands in her mouth and helped her forward.
"Not only was this helpful, but it gave Harriet a great incentive to try walking as often as possible, which is essential as it stops her legs seizing up."
Adrian and Sue quickly developed trust in Yeppa's patient and caring nature towards their daughter.
They attached a lead to the frame, which meant Harriet and Yeppa could go for short walks together.
If Harriet fell, Yeppa alerted them by barking and would help Harriet to her feet by providing stability for her to pick herself up.
"Walking with Yeppa has given Harriet increasing confidence not to worry about falling," says Sue.
And if Harriet's condition is more painful than usual and she is walking more slowly - which happens on colder days - the three-year-old dog merely adjusts her pace to stay alongside.
Yeppa even helps her out of bed by tugging off the covers and gently pulling her arm. She then helps Harriet get dressed.
"Yeppa will gently tug her sleeve or the leg of her jeans to help Harriet," explains Sue.
Nearly half of those with cerebral palsy get arthritis as a result of the extra stress and strain the disease puts on the body.
The heart, veins, arteries and lungs have to work harder and they age prematurely.
Sufferers also have limited strength and restricted patterns of movement.
Even at her young age, Harriet has such painful arthritis in her knees that some days she cannot get out of bed.
When this happens, Yeppa stays on the bed to keep her company.
She also helps Harriet in and out of the car when she goes to school in Tring, Hertfordshire.
One in 450 babies in the UK is born with cerebral palsy. It is caused by damage to the motor centres of the brain, which normally occurs before, during or soon after birth, although in most cases - as in Harriet's - the cause of the damage is unknown.
The condition causes stiff muscles as the part of the brain controlling them is impaired, and this leads to movement and balance problems.
Children with cerebral palsy often have other related conditions, such as learning difficulties and impaired vision, hearing and speech.
"Harriet deals with her disability amazingly well. She says she wants to be able to wear normal shoes one day.
"In total, she's had a year off school - for physio; when her arthritis has been too painful for her to get up; for operations to lengthen her hamstrings; for various biopsies to explore her muscles; and for feet-straightening procedures.
"Yet she's still at the same educational level as other children of her age."
Traditionally, assistance dogs helped blind people but now others with disabilities as various as autism, deafness and epilepsy are benefiting.
Dogs have been taught to help with duties such as opening doors, picking up dropped items, switching on lights, barking to raise the alarm in an emergency, and even warning epileptics when a seizure is coming on.
Now, Yeppa has improved Harriet's walking so much that surgeons can carry out an operation that could enable her to walk independently all the time.
"We were told Harriet needed to reach a certain level of mobility before she could have the operation," says Sue. "Thanks to Yeppa she has."
This sixth operation for Harriet is the most major as it involves surgeons at the Royal London Hospital breaking both her feet, then resetting them in their correct alignment and at the same time lengthening her feet using bone taken from her hips.
"She'll have to wear a cast for six weeks, then learn to walk again," says Sue.
"She has physio once a week now but that will increase to three times.
"The aim is that within several months she'll walk independently. But much depends on Harriet's determination and Yeppa is her greatest incentive."
• Harriet has set up a charity at her school to help it raise funds to assist other children with special needs. Dundale School, Silk Mill Way, Tring, Hertfordshire HP23 5DJ. 01442 822421; www.dundale.herts.sch.uk; firstname.lastname@example.org
How a Crufts favourite helped 11-year-old cerebral palsy sufferer Harriet learn to walk | the Daily Mail