Wait, was she hired to play a character? It kind of makes sense that the character should be in costume and the people in costume shouldn't be able to accessorize as they see fit even if it is a religious item. Now if she was hired to sell mickey shaped ice cream bars then let her wear what ever she wants.
One of the things Disney wanted to avoid was the disheveled look of the employees of other parks or carnivals.
Every employee seen by the public in the park, from the guy selling Hotdogs to the girl dressed as Jasmine, signs up as a "cast member" that has to follow strict uniform and behavior rules.
Showing no religious belief while "in character" is part of the deal.
They used to do that. They finally allowed people to wear their own undies after a rather significant case of the crabs spread from cast "member" to cast "member."
I never thought I'd say something like this, but I'm on Disney's side here from what the video presents. They basically say "no religious material of any kind" - so no crosses or druid robes either.