Why was Maleficent the only creature of her kind in the Moors ?

There's a story that they didn't bother to tell. In fact considering she is the main character of the film we get no back story about Maleficent at all. Where did she come from? Who were her parents? Who is she?

And she shouldn't be called Maleficent because she wasn't evil. Rather she was justifiably angry at what was done to her. If not for her watching over "Beastie" and intervening when necessary the child would have died from neglect. So even in her anger she was still a good person at heart.