Interesting fact: 3rd level Fly has the same text and Celia is a sylph. Assuming she's the 3 HD baseline version, she casts as a 7th level sorcerer. She has demonstrated her ability to use 3rd level spells, but as far as I can tell, we have only ever seen her cast Lightning Bolt – which leaves a slot open for another 3rd level spell known. Now, Fly is a weird pick for a creature with 90' (good) innate flight, but she doesn't need anything we don't know of to be able to fly with a heavy load for more than half an hour a day.