A friend of Josh's, Sabrina is a major in Chemistry and Pharmacology.  She's a little overweight, but is obsessed with her appearance.  Or, rather, obsessed with how ugly and fat she thinks she is.
Truthfully, she's fairly attractive, but takes poor care of herself, which doesn't help her much.
She thinks that if she doesn't force people to do what she wants, they'll ignore her and choose someone 'prettier' to be with, so she feels fully justified to use crying, begging, browbeating, and even emotional blackmail to get attention or other things she wants.
She's even threatened suicide to get a date, a charge she denies totally.