Jeannine has it pretty easy as the new girl in school. She's definitely more Zooey Deschanel than she is the designated ugly friend. She's attractive and self-deprecating, interpreting her own zodiac sign, Gemini, as meaning that she is "two-faced and unpredictable" (20.66). Don't go into horoscope writing, Jeannine, because this is completely the opposite of your personality.
Jeannine's patient, flawed, and human, even if she does verge on being a character who exists just to teach the main character, Conrad, a lesson. Even though they form a romantic relationship, she's just as much a mentor as she is a girlfriend. For one thing, she's more experienced. She doesn't judge Conrad, and she's even happy to tease him about how slow he was asking her out. He says he's swift, and she remarks. "September to February? Is swift?" (20.77).
The most important lesson Jeannine teaches Conrad is that no one is perfect. At the end, she reveals that she moved to town because she caused a lot of trouble in her old town stealing, doing drugs, and being promiscuous.
But Conrad still cares about her, which suggests to him that even though he is flawed, people can still care about him, too. It's so heartwarming it hurts.