If you put the focus on her head the nose and ear are at different distances so one or the other may blur slightly. Just a guess but you might try putting a small sphere in the middle of her head, obviously small enough that it can't be seen. Select the sphere then in render options set the focal length to the current selection. It'll probably come closest to focusing on the midline of the head. On the other hand...as I type that... The eyes are probably where you want to tightest focus so... Select the eyeball...the one with the tear. Again, in render options set focal length to the current selection.