Your girlfriend is seeking control in her life. She feels that her only power is in what she does with her weight because no one else can control that. Its all about self-esteem. For me the answer was Prozac which made me feel better about myself...but there were a lot of side affects. What she's doing now can cause major damage to her body. She really needs to see a doctor...but meanwhile you might try calling a woman's help group or log in on an eating disorder web site.