One of the witnesses ,Mary Brwon claims that the witch takes on a half woman and hairy horse shape. Has anyone heard of a KElpie. a scottish waer sprite that predicts a drowning. Not very nice..
Still sounds like a centaur to me.
(Save me the centaur aisle, would you?)
The kelpie didn't predict drownings, they lured people to their death, appearing in the full form of a horse, not as a half-horse.
SF-FF, as an Anthony fan, you might be interested to know that a close kin to the kelpie is a faerie known as the Phooka, who also takes horse form, and is also known to lead travellers to their doom. :bg: