Qualify

1: I could be wrong, but I don't think there's any such thing as Major or Minor NOTES. Chords, scales, intervals, & other such RELATIONSHIPS, yes. But not single notes. And yet they show up over and over and over in the book. Considering that the entire science system of the Atlanteans is music-based, I would have guessed they'd know music theory better. And for the Yellows having a system based on sharps, they're sure singing a lot of natural notes.
#2: Mezzo-sopranos have a vocal range between sopranos and contraltos. They are not higher-sopranos. So if the main character is surprised by how high of a note she can sing, the logical conclusion is NOT “Oh, wow, I'm a mezzo like my mother.” Even when they CAN hit the high notes (and some can), that is not where they are most comfortable. But Gwen is, so I doubt she's a mezzo.
#3: I realize teenagers are, shall we say, less discriminating in their attention, but Gwen is bugging me with the way she drools over allllll the hot guys. “I'm blushing. My knees are weak. My IQ just dropped to the floor.” Even when she gets a boyfriend who has been her crush for years. Even when she's in a qualify-or-die scenario. Even when the hot guys are aliens and/or people she doesn't even know. Yup, still have to drool over every shirtless, chiseled body & every beautiful face, to the point of turning into a blithering idiot.
#4: Gwen's sister should have been cut. Good grief! And since the aliens wouldn't have made an exception for Gwen's rare voice, they wouldn't have made an exception for her sister with much less cause.
#5: I totally agree with the other reviewers who mentioned the high improbability of all of Gwen's friends and enemies making the cut. And the annoying “Gwen always has the answers and the skills” issue.