She was also found guilty of seven murder attempts involving six other babies there but was cleared of two additional charges of attempted murder. The jury was unable to reach a verdict on several other charges.
Officials at the Court of Appeal said Friday they had received an application for permission to appeal against the convictions.
Typically, applications for permission to appeal against a crown court decision are considered by a judge without a hearing. If the bid is refused, the guilty parties have the right to renew their bid at a full court hearing before two or three judges.
Letby’s motives remain unclear, but the scale of her crimes pointed to intricate planning.
Letby, who refused to appear in court for her sentencing or to face an outpouring of anger and anguish from grieving parents, was accused of deliberately harming the babies in various ways, including by injecting air into their bloodstreams and administering air or milk into their stomachs via nasogastric tubes.
She was also accused of poisoning infants by adding insulin to intravenous feeds and interfering with breathing tubes.
Judge James Goss imposed a rare “whole-life order” on Letby, who he said acted with “malevolence bordering on sadism.”
Only three other women have received such a harsh sentence in the United Kingdom.
The British government launched an independent inquiry soon after the verdicts to look into the wider circumstances around what happened at the hospital, including the handling of concerns raised by staff.