A few problems with the film(spoilers)
Melody seems to become an obnoxious narcissist after her diagnosis. She seems to abandon all morality. She stops being vegetarian, starts stealing, throwing boxes and garbage out the window, seducing a married man..
30 minutes into it, I was hoping she would hurry up and die already..
Cookie shows up, a couple of days after they first met(where Melody didn't display hint of personality, let alone a romantic interest in Cookie), with a pizza and wine, presumably hoping to get Melody into bed. And later we find out Cookie is not even a lesbian, she's getting married to her violent boyfriend.
She flirts slightly with Roscoe the delivery guy, and when he shows up days later with flowers, she doesn't hesitate to jump into bed with him, knowing well he is a married man. Obviously that's mostly his fault, but she doesn't seem to have any problem with him cheating on his [pregnant]wife
Melody is just not a very likable character.