Well... in response to the first question: yeah, Mandy's a bitch, but there are other things suggesting she's hideously insecure.
I mean, she obviously values external appearances a lot, or at least sees them as making someone worth something. Maybe she feels that that's all she has going for her?
Furthermore- the eating disorder stuff. You don't hate yourself enough to starve yourself or feel so guilty about eating that you make yourself sick because you have wonderful self-esteem.
Finally- she's a bitch and a bully- as we've seen with her treatment of Beatrice. Beatrice is quite clearly WAY down on the social food chain, and isn't really competition for Mandy in terms of the things she values- such as looks, or getting attention from boys. Lola appears to be more on her level, right? Yet she won't directly take on Lola- she hits out at the weak kid who can't stand up for herself.
I mean, how many people bully others just to make themselves feel like bigger people? Looks like Mandy's one of them.
As for her confessing all to Jimmy: she felt down and out and depressed, and like the world hated her. Probably like she had nothing to lose. In that situation, I'm guessing you'd either be too tired to put on an act that you're some bitchy kind of confident person, or she just didn't care who saw her vulnerable side hanging out.
That's my theory, anyway.
