She wanted some of the shots "moody" and "dark"

RustingInPeace

used 580exII flash and radio popper

dogwood

That first shot looks out of focus. Long exposure? I also think her right leg is distracting and would crop it mid-thigh.

On the second shot, your light is too low-- check out that unflattering nose shadow. It's much more flattering in the first image.

The light on the third image is kind of harsh. It really highlights her left nostril and that line to the left of her mouth.

I get what you're trying to do here and it is possible with one light but you might consider a modifier like a gridded strip dome to really create mood while still keeping the light under control. And don't forget hair and makeup can create mood too. Here's a sample of what I'm talking about (single light in a gridded strip dome):