Hi Chris, Kira, and the rest of your family.
How fortunate to have a sibling match. It shows that luck is on your side, but by reading about transplants and asking questions you'll make your own luck too.
One thread you might useful is named
How do you spend your time when you're stuck at home or in the hospital?. There's a lot of boredom involved, especially for kids who are used to being active all the time, so I suggest letting Kira help you decide what toys, games, or gadgets would be suitable to have with her. Perhaps she can prepare her own backpack for this purpose.
Staying in touch with friends is very important for this age group. Phone calls, email, texting, even setting up a blog. Any method might work, but chances are it'll take your effort to get the ball rolling and not let her friends forget to keep in touch when she's not there in person. Find out the rules for visitors (days, times, number of visitors, age restrictions) so you can let people know if they can visit or should just phone/text/email. Warn everyone that Kira won't always feel up to having visitors or talking on the phone.
If she'll be able to have Internet access, there are a lot of websites with free age-appropriate "Flash games". For example,
Cancer Smash is one I can recommend. If you have a tablet like an iPad there are similar games available, many of them free. These are good gaming choices (if she's allowed to have electronics with her at all) because there's an endless variety of types of games, and most are easy to play for a few minutes now and then, rather than needing a longer stretch of time and attention than a transplant patient is likely to have.
Nobody wants SAA, but Kira's got everything going for her. A special shout-out to Kira's brother for already being a hero!