In short, yes. It ruins the childlike, happy, pixie dust magic that you had as a kid.
BUT! But, working for Disney provides it's own, amazing, inexplainable magic that makes up for it, in my opinion, 1000%.
There's always
Disneyland which always feels the same "magicalness", to me. Then at Disney World is where I work. I still love visiting the parks. I love the "cast member" inside me that just has to pick up trash and answer questions for the guests. It makes me feel knowledgeable. I love the backstage magic they provide. I loooooove the perks. I love learning how a huge company runs. It's all so amazing.
Don't allow fear of "ruining magic" to prevent you from getting a job and a fantastic learning experience. I promise, there's enough magic in Disney to go around. If you really love Disney enough, you'll find happiness any way you experience it. At least, that's been my experience.
Good luck with whatever you choose! I hope whether you find magic, or create it, you love what you do! That's my advice to your daughter.