Hmmmm so I'm pretty new at this Pitch Madness thing, but I'm pretty good with loglines, and they're pretty similar right? That's what I hear, anyway.
The new guidelines for Pitch Madness say 35 words max, and yours right now is 31 if you count hyphenated words as one, or 34 if you count hyphenated words as separate. Either way, you're golden there!
I like to make sure the following criteria are present for my loglines: an interesting character with a passion, an incident that affects the character, a risky/difficult goal for the character, something/someone in the way of that goal, and a risk of disaster expressed in terms of the previously stated passion.
So looking at what you've got here...
Trapped in a nightmare, fifteen-year-old Lucy Nightingale must face warped laws of physics, random explode-y things, and possible death in order to defeat her Dreamon. Otherwise, she'll never wake up again.
I think this pretty succinctly sums up the gist of your story (I say, not having read it). As far as the "Dreamon" thing goes, maybe you could reorder the sentence a little to clear things up. Like...
Fifteen-year-old Lucy must face warped laws of physics, random explode-y things, and possible death in order to escape from the nightmare a demon has trapped her in. Otherwise, she'll sleep forever.
Or something like that?