Melanie- a bit of a diva at times?

Hello. I found this movie entertaining. While I agree that Melanie's boyfriend, Justin, seemed to take her for granted, I found Melanie to be a bit high-maintenance at times. While I adore Lacey Chabert as an actress, I thought the Melanie character treated Dean badly at times, before they realized they were in love. There's one scene in which poor Dean goes out to check on the car, and he comes in covered in dirt, having fallen, after trying to push the car, or something like that. Melanie asks him what happens, and he explains. Instead of giving him any sort of sympathy or thank you for all he is doing, she immediately asks: "Did you call the rental car company?" My thoughts were, "This poor guy is doing everything. Why couldn't she pitch in and call the rental car company?" In another scene, he passes on some news via Justin, and she seens to take out her frustration (with Justin) on him. He even makes a comment like "Don't shoot the messenger." I don't know- I thought Dean was very patient and kind, and at times she wasn't as kind back to him. Did anyone else have this opinion?