Hello Kristinia,
Mickey's Not-So-Scary Halloween Party is one of the few times adult Guests are able to come dressed in costumes, to Magic Kingdom Park. Disney Parks Moms Panelist Jane received some wonderful recommendations after speaking to a Cast Member about costume guidelines when planning for Mickey's Not-So-Scary Halloween Party:
* Costume should be kid-friendly
* Costumes should not be obstructive, offensive or violent
* Costumes should not drag on the ground
* No sharp objects, pointed objects or weapons that could be easily mistaken for an actual weapon
* Mask may be worn, but they must not obstruct vision and eyes must be visible at all times
While Mary Poppins, is a practically perfect costume idea, okay she is one of my favorite, you sister may want to leave Indiana Jones' famous accessory at home. I can not guarantee it would not be confiscated. Instead, think outside the box and use a field bag with a king cobra sticking out of it, or replicate one of the treasures or famous scenes such as the monkey brains or the Holy Grail or the gold idol from Raiders of the Lost Ark to carry in as an accessory. With his famous hat and all to well known button up shirt and khaki pants, she is sure to be recognized as the famous archeologist.
If I can be of any further pixie dusted assistance feel free to ask and may your upcoming stay at Walt Disney World be filled with 999 happy haunts and many magical and memorable moments.
Amy M*o*