Who is the best doctor, who specializes in cystic fibrosis, in the world?

Here are several options for adults (I am making that assumption, correct me if I am wrong). If you have a specific location in mind, let me know, I might have some ideas.
San Francisco UCSF
Denver National Jewish
Baltimore Johns Hopkins
Pittsburgh University of Pittsburgh

According to an essay on making health care better in Atul Gawande’s book, Better: A Surgeon’s Notes on Performance, the CF treatment center with the longest survival for its patients is the Minnesota Cystic Fibrosis Center at Fairview-University Children’s Hospital in Minneapolis. The director was Warren Warwick, who has made a career out of finding out how to do things better.

You can read the actual essay here.

Other centers have been studying what Warwick has done in Minneapolis so that their numbers improve also, and the CF Foundation freely lists center data on its site at http://www.cff.org/LivingWithCF/CareCenterNetwork/CareCenterData/ so you can compare success rates. You or she will need to register with the site in order to have access to the data, but as someone with CF she should be registered there anyway. You might start by comparing the sites listed by @shilolo.

CF.org points out that the best centers have these goals:

* People with CF and their families are full members of the care team;
* People with CF will attain normal growth and nutrition status;
* People with CF will receive early diagnosis of infections and respiratory therapies that keep lung function steady;
* To decrease the spread of germs between people with CF;
* To prevent complications and/or to diagnose and treat them early;
* To provide care regardless of race, age, education or insurance coverage; and
* To support all transplantation and end-of-life care decisions.

I wish her good luck and hope she can find a center or a doctor with whom she can work. Treating CF is a two-way partnership and she should be able to talk to her doctor about why certain decisions are being made and have some input into what actually happens.