I like the "lighting glow" effect placed on the face, hair and arms and parts of the background. It's very lovely contrasted with the partial darkness throughout the piece.
The female's expression is deep and wonderfully calm--as if she is quietly pondering or reflecting about something.
The folding of arms, her "balled up" position (by grouping her legs and arms together and resting her chin near her wrist), and her face pointed away from direct view of the observer coupled with the absence of a smile, suggest she may be worried.
But she does not appear frightened at all. Now I am wondering what may be weighing down on her mind.