I read this book back in 2004 and it's about a girl, I think her name was "Rain" and she was the best horseback rider/warrior in a tribe of women from the Amazon. Her mother was raped by something like 100 men, so she was never accepted by her mother.
So the society is of all women who only use men for reproduction. I think "Rain" fell in love with a man named "Michael." I think the title was just one word, or "The" something. It had a dark cover, with some blue on it, and I think the girl's face on it.