Hooray for a 1st time trip to Disney!!! I'm sure your sister will have a magical time!!
As far as expense go, our expense check covered all our expenses. We did eat breakfast and dinner at GKTW so that cut down on expenses!!
Another Wish Family just asked the same question (what do you wish you had know before your wish trip). Here is my respones:
Our #1 tip is keep in mind that Give Kids the World is a wonderful place full of great activities!! If we could do one thing differently we would have spent more time at Give Kids the World!! I mean we only got free Ice Cream once... come on that's pathetic!!!



Another important tip is if you want to go to all the parks you get free tickets to you will probably have to go to 2 parks in 1 day (unless you get more time in Florida than the standard time).
Tip 3 -- There are lots of really great restaurants but you need reservations for them, so I visited the food thread on the DIS and decided which restaurants we wanted to visit then scheduled reservations.
Tip 4 -- Give Kids the World suggested to us that we have breakfast before we leave and dinner when we get back since meals are free at Give Kids the World. That worked great for us.
Tip 5 -- Make a Plan -- Talk to everyone who is going to see what is on their must do list. Make a rough plan (that is flexible) which includes everyone must do's.
Tip 6 -- Read the Make a Wish Thread and Wish trip reports to use as resources.
Tip 7 -- Universal seems to really roll out the red carpet for many of the families who made Trip Reports (including my family) so save time for these parks if your family is interested in the attractions they have there.
I hope these help!!!
Make A Wish and Give Kids the World really is on top of everything so even if you don't have lots of time to plan or read trip reports they will walk you through everything!!!
Happy Planning,
Madeline