I agree, you have every right to be angry about the situation. If you were perfectly ok with it right away, there would be something wrong. In time, you may make peace with the situation, but it is something that will ALWAYS nag at you. Don't feel bad for feeling that way.
Just to shed some light on a CFers life, my husband was born in 1980 and did ok for the first year while he was exclusively breastfead. He did have some problems, but they ALL came to a huge head when he was taken off the breast. He was diagnosed at 18 months after numerious bouts with pneumonia, hospitalizations, rectal prolapse, weight loss... (you name it, he encountered it pretty much). He got on meds after the diagnosis and made steady progress.
He is now 25, will be 26 in October. He will be graduating from Washington State University this May, we have been married for almost 4 years, we have triplets on the way, he is looking for a job right now with an international company, his weight is up and he hasn't been in the hospital since he was 20. He does do his treatments everyday (The vest and pulmozyme, and tobi when he has a lung infection) and concentrates greatly on what he eats to maintain his weight... but he is happy, successful and tells me all the time he has things he never dreamed of in his life, a wife, he's going to be a father, a college graduate...
With all the new medications and technologies, the chances are better than ever for your granddaughter. But it's still ok to be angry and upset. Just know that a "real life" (what's normal anyways????) IS possible for her.
If you have specific questions for us, ask a way, we're here to help you out with what we know, our own personal experiences with CF or a loved one with CF and make you feel a bit more comfortable about a situaiton you can't change. Big applauds for coming on here, what a great grandfather you are!