What a fantastic idea! I hope there is such an organization, and I hope your great geandmother-in-law gets her wish. I have heard people can donate miles on airlines for people who are sick and need to travel for medical care. I wonder if there is not an organization who grants such wishes if you could you write a letter to the airlines, if she needs a flight, and to a hotel chain in the area, if you could get some sort of great deal for her? It would take a little work, but it could be great PR for the airline or hotel. The biggest problem with the airlines is they now fly incredibly full, so there is very little space for standby.
Also, another idea, almost all the hotel chains give free nights if you open there credit card and waive the annual fee the first year. I think you were on my Q when I asked about opening a new card. I did open the marriott card and had four free nights in the end, I am very glad I did it. Same with the airlines you can many times get a free flight if you open a card, or get a free companion ticket if you need to fly with her.