Overgrowth by Mira Grant

"Since she was three years old, Anastasia Miller has been telling anyone who would listen that she's an alien disguised as a human being, and that the armada that left her on Earth is coming for her. Since she was three years old, no one has believed her. Now, with an alien signal from the stars being broadcast around the world, humanity is finally starting to realise that it's already been warned, and it may be too late. The invasion is coming, Stasia's biological family is on the way to bring her home, and very few family reunions are willing to cross the gulf of space for just one misplaced child. What happens when you know what's coming, and just refuse to listen?"--Publisher.

See http://seananmcguire.com/bio.php Seanan McGuire won the John W. Campbell award for the best new writer at the 2010 Hugo Awards. She uses the pseudonym Mira Grant to write science fiction/horror and the pseudonym A. Deborah Baker to write the "Up-and-Under" children's portal fantasy series.