My experience with my son and "tune ups" has been a blessing so far, he is 12 months old and we have already had a few. And yes he has a port but he only cultures staph! I have never looked at it as the beginning of the end, hell it's been a fresh start every time for us! Sometimes with CF, they need that extra boost and sometimes a "tune up" can do just that. Are you sure there wasn't more to it, like low PFT's? Just curious!
Also, didn't you post not to long ago about withholding treatments from your daughter? Well....not to bash you or anything, but that just might have come back and bit you. Not doing treatments and not progressively fighting this disease can definitely land you in the hospital. So as "tune ups" cant always be avoided, not doing the prescribed treatments doesn't help!
Good luck and I hope you make the best decision for your daughter.