I saw her audition last night on youtube and I don't remember her either -- and I've watched every American Idol season since Season 1.  She definitely seemed "off" but it's so hard to say in what way someone is off.  Sometimes it's just something minor and harmless -- like being eccentric -- and sometimes it's much more of an inner, more dangerous, kind of disturbance, like stalking someone.  Unfortunately, she turned out to be the latter.