She's lean not what I would call skinny. Remember Alizée is a little woman who stands just barely over 5'3" so normal for her looks like she's anorexic. The easiest way to check to see if she is too skinny is look closely at her face. Now we know how hard that is for the members on this board.
If she starts to get the hollow or drawn look in her cheek area then start getting concerned.