The Shaktra — Christopher Pike

Ali Warner is thirteen years old.
She's already saved one world.
Now she must try to save another.

Ali recently discovered that she is not an ordinary teenager but actually Queen of the Fairies. Reclaiming some of her magical abilities, she has taken possession of a mystical talisman whose powers she has barely begun to understand. She has saved the Earth from an invasion by elves and other creatures from the elemental world that lies parallel to our own.
Now Ali searches for her missing mother in the elemental world, accompanied by a troll, a leprechaun, and Ra, a mysterious African teen whom she met on the icy slopes of Mt. Kilimanjaro. Ali feels a strange connection to the young man, but does not understand why. They grew up separated by half a world.
Attacked by nightmarish creatures, a wounded Ali and her friends are rescued by Drash, a young dragon with an inferiority complex. From Drash, Ali learns that the elemental world is on the verge of destruction at the hands of a sinister being known only as the Shaktra.
Meanwhile, on Earth, Ali's friends Steve and Cindy investigate the beautiful and bewitching Sheri Smith, who is somehow connected to the Shaktra. Too late, Steve and Cindy discover that she is not human at all . . . .
In a secret ice cavern hidden on a massive island that floats through the elemental heavens, Ali discovers the true relationship between humanity and the elementals--and the hideous nature of the enemy she must face.
Ali Warner's quest will not be complete until either she or the Shaktra is dead.