Also, the gunman was behind her when he fired. If a bullet did hit her, why would the force have pushed her back instead of forward, into the front of the roof?
Watch this Penn and Tellar vid about the JFK Assassination to understand how a head responds to being shot (relevant stuff is at 1:15):
Tale of the Tape [Ace]: Supposedly you can see her shawl blown back by the bullet here, though my computer is acting too weird for me to see it: