Princess Protection Program

Princess Rosalinda MarÃ­a Montoya Fiore (Demi Lovato) is about to be crowned queen of the small nation of Costa Luna. General Kane (Johnny Ray Rodriguez), the dictator of neighboring country Costa Estrella, invades her palace with his agents during her coronation rehearsal, and attempts to capture the royal family and take over the country. Joe Mason (Tom Verica), an agent of the Princess Protection Program, a secret organization funded by royal families that looks after endangered princesses, whisks her away to safety via helicopter. Kaneâs agents, however, succeed in capturing her mother, Queen SofÃ­a.
The Princess Protection Program hides Rosalinda in Masonâs home in Louisiana, where she is to masquerade as a typical American teenager named Rosie Gonzalez. She meets Mason's daughter, Carter Mason (Selena Gomez), an insecure tomboy who works at the family bait shop and dreams of going to the homecoming dance with her crush, Donny (Robert Adamson). Though Carter initially treats Rosie with barely masked hostility, she warms up to her after Rosie explains her situation, and the two become best friends. Carter teaches Rosie to act like a typical American teenager, and Rosie shows Carter how to disarm those that scorn them (especially resident mean girls Chelsea and Brooke) by behaving as a true princess. Rosie soon becomes popular at their high school.
In an attempt to trick Rosalinda into exposing her location, General Kane announces false plans to marry her mother. Brooke discovers that Rosie is in fact Princess Rosalinda from a magazine she reads for Spanish class. She and Chelsea confront Rosalinda and threaten to expose her, but they agree to keep quiet if Rosalinda drops out of the vote for Homecoming Queen. Brooke and Chelsea also ruin the dresses Carter and Rosalinda were going to wear for the dance. Rosalinda reads of the pending nuptials in the magazine and tells Carter that she has decided to return home. Knowing Costa Luna is still too dangerous, Carter secretly devises a plan to pose as Rosalinda and then use herself as bait to lure Kane into capture. Carter calls Mr. Elegante, Rosalinda's royal dress maker, for help with her plan. He tells Kane that Rosalinda will be attending the homecoming dance and will be wearing a blue dress that he actually sends to Carter. In the meantime, Rosalinda agrees to stay for the dance in order to help make the event special for a group of friends, the group of girls wear masks, which helps Carter disguise herself as Rosalinda.
According to plan, Kane and his agents mistake Carter for Rosie and lead her to Kane's helicopter the night of the dance. However, after winning the Homecoming Queen title and dedicating it to Carter, Rosalinda discovers and ruins the plan by exposing herself to Kane, insisting that it is not Carter's fight. Fortunately, agents of the Princess Protection Program, including Mason, have been waiting inside the helicopter and rescue both girls. The P.P.P. agents quickly apprehend Kane and his henchmen and turn them over to the international authorities.
Rosie is crowned Queen of Costa Luna with Carter, Mason, Ed, SofÃ­a, and Mr. Elegante in attendance.

Question: What do the girls wear to the dance to disguise themselves?
Answer: masks