Well she's lost it.
She hasn't, she is just extremely hurt right now >.< you don't understand what Jason does. He gets into your head and makes you feel special, makes you feel that you are the only one that has ever truely mattered to him. And thenhe looks at another girl, getting you a bit jealous buthe assures you that you are still the only girl for him, making you love him that extra bit more. Once he has a hold of you, he just fucks you over until you're this little broken husk. Once that's done he will leave you, and make you hate yourself. Amy isn't crazy and hasn't lost it. She has just experienced Jason.