Hello there, Terry! Welcome to the Disney Parks Moms Panel and thanks for sending over your question!
Walt Disney World Resort makes Guest drop-off and pick-up as simple as possible at all four Theme Parks. The procedure is a bit different at
Magic Kingdom, though. The designated drop-off and pick-up location for Magic Kingdom is actually located at the Ticket and Transportation Center. Upon arrival to the Ticket and Transportation Center, simply let a Cast Member know that you will be dropping off your sister-in-law and they will direct you to the designated drop-off location or follow the signs leading to the designated drop-off location. Once you have dropped her off, she can then utilize either the Monorail or Ferry Boat to get to the front gates of Magic Kingdom.
There are courtesy wheelchairs available at many drop-off locations that may be used to get to the wheelchair and ECV rental locations within the parks. ECVs and wheelchairs may be rented at Mickey's Gift Station at the Ticket and Transportation Center and at Wheelchair Rental at the entrance of Magic Kingdom. However, these are first-come-first serve so they are never guaranteed. It should also be noted that ECVs and wheelchairs may only be used within the park in which they are rented and must be returned prior to leaving said park. If your sister-in-law is going to require an ECV or wheelchair rental throughout the duration of your stay, I would actually recommend renting one through a
Disney Featured Provider. That way, she will have access to a mobility assistance device at all times during your vacation. These rental companies also allow pre-orders and even deliver to all Disney Resort hotels!
Hopefully this provides more information regarding the drop-off and ECV and wheelchair rental process!
~Wyatt