Glenowen; or The Fairy Palace — Eleanor Sleath

Ever wish you were someone else? Katie falls in love with a handsome fairy boy, Colin, and wants to be a fairy herself. In this third book of the Crystal Palace trilogy, three human girls (Karina, Nicole, and Katie) return to Fairyland to visit their fairy folk friends and to see how well the reforms they had mediated were working.
The Sorcerer gives Katie beautiful fairy wings, but he is jealous of the human girls' growing influence on the king and plans to humiliate them. His scheme is interrupted when insects (huge to the fairies) attack Fairyland.
Urged on by their evil tarantula leader, swarms of enormous, angry insects and spiders descend upon the fairy folk. Their goal: to destroy Fairyland, before turning their sights on the human world.
A story of envy and forgiveness, courage and cooperation, friendship and caring, The Crystal Palace III: The Fairy War demonstrates the power of love and working together toward a common goal. The girls learn about their prejudices and jealousies, as well as their courage and ingenuity, as they solve the very human problems they face in Fairyland. In the end, they realize they don't need the magic of Fairyland. They are ready to navigate the world on their own.