Lily Choy was sentenced in 2011 to six years in prison after she was found guilty of manslaughter for a second time.
Her first conviction was overturned by the Appeal Court because the trial judge gave the jury incorrect instructions.
In her most recent appeal, Choy's lawyer argued that the judge did not properly consider some of the testimony or findings from medical experts.
But the appeal judges concluded there was nothing wrong with the trial judge’s handling of the evidence or her conclusions.
The boy died on Jan. 27, 2007, after his head hit a toilet and doctors couldn't control the swelling in his brain.