Hello Leslie! Welcome to the Disney Parks Moms Panel.
A Walt Disney World Resort vacation is about spending Endlessly Magical Moments with your entire family. Many of my favorite moments have occurred during our dining experiences at many of the restaurants on property.
In my experience, I have never heard of or personally seen any instance in which a Guest, as part of an
Advanced Dining Reservation, has been expected to redeem a Disney Dining Plan credit when they are not eating at the restaurant.
In fact, even with the
Disney Dining Plan, I could choose to redeem my credits whenever I chose and decide to pay out of pocket for a meal to save credits for an alternate dining experience.
The point is the Disney Dining Plan may be used as you see fit and is never "automatic". The server will usually ask you when you are first seated or before the bill arrives if you will be redeeming any Disney Dining Plan credits. Only after that will Disney Dining Plan credits be put into play for your dining experience.
As far as not eating, Cast Members at Walt Disney World Resort Dining Locations are incredibly understanding when it comes to suiting the nutritional desires of their Guests. If your Mother-in-Law cannot eat during the meal, she will be welcomed to experience the Endless Magic with your family, regardless. Especially if everyone at the table is having a full meal, themselves.
I have made Advanced Dining Reservations for dining locations and ordered only drinks or a single dessert and have never had any issues with redeeming Disney Dining Plan Credits or not ordering full meals.
Bon Appétit!
~Todd