My living family tradition (from both sides of the Ohio as early as the 1800's) kept the phase, 'he's agrinin' like a wampus cat' and 'quit grinin' like a wampus cat!', and it was thought that a wampus cat was like the cat that ate the canary as the term was used as such. No knowledge of any mythical beast was known of.
I have found the term cited once in a dictionary of slang which said that wampus cat was the same as Cheshire Cat only the term was used in the area to the south of Cheshire, which means that the term is from rural Western England and was brought to America by settlers who evolved a new meaning for it. The phase 'looking like a cat chewing gravel' was also used and that would support this earlier posting (1851- They sed that he and his wife and children had their faces so wrinkled up and turned cater-wampus like, that the skeeters couldn't lite on um long enuf to bite. "Spirit of Times.")
As for the mythological wer-woman, I think that the person who made that up was talking like a man with a paper nose.