The court found that the threat to kill was "mean and vicious" and was directed at children.
"However, the sending of the letter appears to have been a spontaneous decision and a reflection of immediate anger, rather than part of a campaign to terrorise," the Court found.
The three Justices, Tony Randerson, Alan MacKenzie and Raynor Asher found that although the woman was worried about the threat, the children laughed when she read it out.
"The threat was contained in a single letter which Mr Faaleaga said, at the trial, he immediately regretted sending.
"He gave evidence indicating that he had tried to stop the letter and apologise to his sister. We do not refer to this in the context of remorse, but rather as a factor indicating the spontaneous and one-off nature of the threat."
The Justices found that he would not have been able to carry out the threat for years because he was serving a prison term.
They also recognised that Faaleaga had regretted sending it.