I wouldn't plan on work shoes until she arrives, as they vary depending on location. Case in point, in Tomorrowland attractions we all wear black tennis shoes, but my roommate who works in Frontierland has to wear hiking boots. I really doubt
Crocs would be appropriate regardless, both in terms of style and material - remember Attractions often means working with heavy machinery that has the potential to injure people.
She'll find out what shoes she needs specifically her first day of work after Traditions (I remember asking them at Traditions but they couldn't give me a very specific answer). If she needs tennis shoes (the word they always use to describe them is "polish-able") I highly recommend Sketchers Shape-ups - they're my work shoes and there's so much padding and comfort that my feet never hurt, even after working for 12 hours.
Hope this helps!