I believe you'll find that "chupa" -> "suck", and "cabra" -> "goat".
This might explain why such a woman might earn that epithet.
And "cabra" is certainly from Latin "capri"... as in
"caprimulgiformes", the order of birds known as "the goatsuckers".
These birds (which include the whippoorwill) are very unusual-looking;
maybe we should compare their appearance with what the chupacabra
"witnesses" have described.
-- John Porter jporter@btg.com