[@Vocab] I doubt an airhead would make a good sniper. Maybe make the flaws more in her interpersonal relationships or something, because physical shape is a must for a sniper. Maybe she can only "focus on one thing at a time."

She easily "focuses" on things, so she can only handle doing like one thing at a time. If she's watching the action, she can't hear someone talking beside her. If she's talking to someone, she won't notice an explosion going off behind her. 

:D