I think she believed the hype.
I'm having a kind moment here, but I do think it must be very difficult aged 19/20 to have countless people saying how awesome you are, then as soon as you're off the hit show, no one wants to know you.
Truth is the girl is a dreadful actor... I've never seen a more wooden, bland performance than that of her portrayal of Marissa on the OC. However the show was huge, the industry told her she was a big star... and now she's been bumped for the High School movie types.
I reckon I'd wanna throw back a few bevvies too if I had all of that Hollywood crap to deal with