Hi Allison!
Watching the Magic Kingdom fireworks show Wishes from the California Grill is awesome. The California Grill is very popular, especially if you want to see Wishes from a table while dining. You should definitely make an Advanced Dining Reservation! I know you asked about having a desert only, but I would recommend having an entire meal. Their food is fantastic! If you just want to plan for desert, then subtract 60 minutes from my recommendations below.
There are two options to view the fireworks:
- From your table and hopefully one in front of a window facing the Magic Kingdom
- From a private balcony
If you think your sister would rather watch from their own table, then I suggest making the reservation for two hours before Wishes. I know that sounds early, but I would plan dinner taking 90 minutes. Your sister will also have to request a table with a view of the Magic Kingdom at check-in and she might have to wait 30 minutes (or more) to get such a table.
The other option is for them to walk out on the balcony. Then I don't think the time of the reservation is as important, though I would still suggest a reservation between 2 hours and 1 and a half hours before Wishes. You could also make the reservation much earlier in the evening and your sister could tour the rest of the Contemporary after eating and before Wishes; with a receipt, your sister will be allowed to return to the California Grill just before Wishes and watch them from the balcony.
Write back if you have any more questions!