The Vanishing Girl - Laura Thalassa
I can't make my mind up about this book. The concept is sort of like one I've read before of the altered children who are super weapons controlled by the government. Though this one is a bit more controlled than the other. Of course, there's the "old girlfriend" problem...at least in her mind. But our heroine is a rebel by alteration, you might say by design. And they don't know quite what to do with her. She's too good to kill off, but she won't quite conform. Then they catch her actually sneaking and snooping and conspiring with the enemy. Then we get the cliff hanger ending. I probably will have to read book #2 to be able to decide about the series.