At times she went a little blue in appearance, a sign that her heart was not functioning properly.
However, her parents Susanne and John, who live in Cheam in Surrey, believe she would not be alive today had they followed advice given to them by the Royal Brompton Hospital.
Ellie was born in 1992, and, as well as having Down's syndrome, was showing all the classic signs of a heart defect.
At times she went a little blue in appearance, a sign that her heart was not functioning properly.
It turned out she had three unwanted holes between two of the chambers of her heart, interrupting the flow of blood.
Susanne told BBC News Online: "It was a very traumatic time, simply giving birth to a baby with Down's syndrome, let alone finding out she has a heart problem as well."
Ellie was referred by the St Helier Hospital in Carshalton, south London, to the Brompton, which had a reputation for excellence in child heart surgery.
'Not in her best interests'
Susanne said: "We had a long discussion with the doctor there - and he recommended to us that he didn't feel surgery would be in her best interests."
Although it was difficult, they accepted this advice, but then had second thoughts, and went back to St Helier to try to get a second opinion.
This time they were referred to Great Ormond Street Hospital, where, following a closer look at the heart using an inserted catheter - a procedure not carried out at the Brompton, the cardiologist said that the operation should go ahead after all.
"What reassured us was the fact that when he met us, he said: 'I'm not interested in her Down's syndrome, I'm just interested in her heart.'"
The operation was a complete success, and Ellie has developed normally ever since.
Susanne said: "She runs like the wind, she's full of beans.
"But there are parents in the Down's Heart Group who have left it too late, and it's a completely different story."