If you are looks to base this book on actual demonology and mythology i suggest you use the internet for a fast search, but i can give you one suggestion, its name is Lilith, It or she if you want to call her that has multiple names, but is known as a child killer or a Night Hag, she is from the Mythology of Ancient Hebrew and from Mesopotamian Heritage, that would make her at least 5000 years old... of course only if you believe in that stuff
