“Things that try to look like things often do look more like things than things. Well-known fact.” ~Esmerelda ”Granny” Weatherwax
Considering that she's beaten elves, vampires (Vampyres), wizards and other witches, it's hardly likely anything could beat her.
Her reputation with scare them stiff, before they even began.
“She'd become a governess. It was one of the few jobs a known lady could do. And she'd taken to it well. She'd sworn that if she did indeed ever find herself dancing on rooftops with chimney sweeps she'd beat herself to death with her own umbrella.”
― Hogfather