Manjit Basuta, a former nurse aged 44, broke down before an American jury after it ruled that she had shaken to death a 13-month-old boy.
The case, which drew comparisons with the Louise Woodward trial, has reignited the debate over childcare laws in the United States.
But last night Mrs Basuta's brother, Amarjit Singh, said: "There will be an appeal, there is no doubt. We won't let this happen to her. She is innocent and there is no way we are going to leave her."
Speaking from the family's home in Slough, Berkshire, Mr Singh said that a mere "five minutes" had changed his sister's life for ever.
"I actually fear for my sister's life. I hope that she has the strength to pull through this - I fear she hasn't. She has to believe in her faith in God."
The British nanny, who now faces 25 years in an American jail, will be sentenced next month. The San Diego court heard how Basuta lost her temper and threw the baby, Oliver Smith, to the ground after he refused to stop watching television when it was time for him to have his nappy changed.
The prosecutor, Dan Goldstein, said that Basuta, who ran a daycare centre in the city, tried to cover up the killing - first by claiming that the boy fell and hit his head and then by blaming a girl in her care for pushing him over.
Mr Goldstein said that Oliver had died from "shaken baby syndrome" in March last year after sustaining injuries to his retina, forehead and brain.
The defence had maintained that Basuta had never shaken the child until after he had collapsed and was unconscious. They claimed that the toddler had injured his head months before the incident and that he had suffered "spontaneous bleeding".
Last night Mrs Basuta's relatives insisted that they would continue to challenge the evidence that had led to her conviction.
"When she set up the daycare centre in America, she was obviously checked out by the local authority. She was registered and everything about her was checked," said Mr Singh, 34.
He added: "There are 32 counts of contradiction when you look at all the evidence in the case. There are so many disputes in the case that she is very shocked that this could have happened.
"We know that a child has been lost and we have never lost sight of that. The fact hasn't been lost with the family."
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