Principal Celestia is the principal of Canterlot High School and one of the supporting characters in My Little Pony Equestria Girls.
Depiction in films
My Little Pony Equestria Girls
In the alternate world that Twilight Sparkle travels to in the film, Celestia appears as the principal of Canterlot High School. When Twilight's stolen crown ends up in Fluttershy's hands, she turns it over to Principal Celestia for safekeeping. Twilight goes to Principal Celestia about this matter, and Celestia explains that the only way for Twilight to get the crown to be voted Princess of the Fall Formal.
At the Fall Formal proper, Principal Celestia congratulates the school students for fixing up in the gymnasium after Snips and Snails trashed it earlier, and she announces Twilight Sparkle as the winner. She later commends Twilight for her role in defeating Sunset Shimmer.
My Little Pony Equestria Girls: Rainbow Rocks
In Equestria Girls: Rainbow Rocks, Principal Celestia first appears walking into the gymnasium with Vice Principal Luna to check on the students making signs and posters for the CHS Musical Showcase. She expresses hope that the showcase will be even better than the Fall Formal, inadvertently reminding the students of Sunset Shimmer's actions.
After the Dazzlings' arrival at the school, the Rainbooms try to warn Celestia and Luna about their true nature, but by the time they are reached, they have already been hypnotized by the sirens' song. Celestia and Luna later serve as the judges for the Battle of the Bands, and the Dazzlings hypnotize them and coerce their decision in favor of the Rainbooms instead of Trixie and the Illusions.
Music to My Ears
Principal Celestia briefly appears in the animated short Music to My Ears. When she catches DJ Pon-3 listening to music on her headphones in the school hallway, she confiscates the headphones and gestures for DJ to get to class.
My Little Pony Equestria Girls: Friendship Games
In Equestria Girls: Friendship Games, Principal Celestia and Vice Principal Luna attempt to raise school spirit with a pep rally before the Friendship Games take place, but they are unsuccessful until Rainbow Dash sings an uplifting song and ponies up.
Later, she gives Principal Cinch, the headmistress of Crystal Prep Academy, a tour of CHS, during which she sees a girl that looks like Twilight Sparkle. Cinch refers to this Twilight as her student, and Celestia believes her to be Twilight's twin sister until Pinkie Pie confusingly explains that she is the Twilight from the human world.
Celestia judges the Friendship Games with Luna, Cinch and Dean Cadance. She denies any involvement of magic in the games, putting her in direct opposition with Cinch. When an incident results in Twilight transforming into Midnight Sparkle, Cinch demands Celestia's forfeit, but Celestia holds her own against the duplicitous CPA principal. In the end, she declares both schools winners and welcomes the Twilight of Crystal Prep as Canterlot High's newest Wondercolt.