In addition to being a decidely old-school method of beating the devil, it was also decidely dumb because--anyone, anyone? That's right! There's no such thing as vampires!
But that doesn't mean there wasn't good reason to believe that the dead might raise. After all, there was this (very circumstantial) eye-witness evidence. MSNBC drives a stake through it:
During epidemics, mass graves were often reopened to bury fresh corpses and diggers would chance upon older bodies that were bloated, with blood seeping out of their mouth and with an inexplicable hole in the shroud used to cover their face.
"These characteristics are all tied to the decomposition of bodies," Borrini said. "But they saw a fat, dead person, full of blood and with a hole in the shroud, so they would say: 'This guy is alive, he's drinking blood and eating his shroud.'"
Thanks to modern science we know that the bloating occurs from gas building up in corpses (yuck!). In any case, why let science ruin it--she was obviously a bloodsucker who deserved a brick sandwich, right?