When does a finger and thumb gun count as a firearm during a robbery

Today in Com. v. Barney, the majority of the Supreme Court of Virginia upheld the conviction of the defendant for use of a firearm in a bank robbery, when the Commonwealth's evidence showed only that she threatened to kill the bank teller and kept her hand in her pocket. Justice Mann, joined by the Chief Justice and Senior Justice Mims, concluded that the evidence was not enough.