Your daughter's symptoms sound similar to a friend of mine's granddaughter's, who was diagnosed at 18 months. She had RSV, upper respiratory infections, but she didn't have frequent/loose stools -- she had constipation issues. The doctor did a sweat test to "rule out CF" and it was high.
DS on the other hand was born with meconium illeus, bowel obstruction and without digestive enzymes, has very loose, shiny stools. His sweat test was normal -- a 32. His blood tests showed otherwise.
Both of these kids have the same genetic mutation.