Earlier this year, I was asked to watch "Mirror Mirror". There was a scene in that movie where Armie Hammer's character is given a puppy love potion, which turns him into a devoted and even obsessive love slave for the queen. When separated from her, all he does is cry and demand to be near her again. Snow White is able to break the spell with a kiss, and all becomes well again.
Jackie Kimball's situation involves no potions, but she is certainly under a spell. In "The Unspeakable Act", we witness a very difficult period of time for her. See, she's in love with her brother Matthew. Now, he doesn't share her feelings, but remains close to her anyways. Most family members would probably be uncomfortable with this knowledge, but Matthew seems to understand that it's all rather harmless.
She meets his girlfriend with a smile and a friendly conversation, but dismisses her as soon as Matthew breaks the relationship off. She sometimes smokes, but when Matthew recommends they quit, she obeys immediately (though she does smoke a little pot later). She accepts answers and advice from him with little to no counter. She even picks his college as her first choice for higher education.
Now, this dependence is a bit unhealthy, but is it really any different than most first love's for teenage girls? The belief that the first love is the only love, that you can't live without the other, etc. She even glows in certain scenes when with her brother. When her therapist asks Jackie is she shares similar feelings for her other brother, she dismisses that idea as disgusting. In her mind, Matthew is more of a lifelong friend than a sibling.
These therapy sessions may provide some answers as to why she acts the way she does, but the movie isn't really concerned with this, and neither am I; WHO is Jackie is more important than WHY is Jackie. She is a very powerful character with a personality that is both naive and wise; always analyzing herself and others, but still stubbornly holding on to her own hangup. She's my favorite teenage girl in a movie since the lead in "Juno".
In the end, this is no fairy tale; a kiss won't break the magic that possesses her. This case of puppy love may never quite be understood (even by her) or even something that she fully gets over - who forgets their first love? - but I have a feeling that she'll be ok. There are lots of fish in the sea, and lots of seas in the world; once she moves out, she'll understand.