All's Fairy in Love and War: Avalon Web of Magic Book 8

Kara discovers two goblins who have fallen through a portal into her bedroom closet. In her attempt to return the pesky creatures to the fairy realm she falls through the portal smack into the middle of a huge war. Kara meets Queen Selinda who appoints her a Fairy Princess and assigns her the impossible task to put an end to the war using her diplomatic skills.