cf carrier

Hey ladies... need some reassurance...
Three years ago when I was pregnant with my son, I found out through a genetic screening that I was a carrier of cystic fibrosis.  My husband was tested using the same screening and his came back negative.  So we were told that since only one of us was a carrier the baby would be fine, worst case would be a carrier like I was.  So he was born and was totally fine, and I didn't think anything else of it.
Fast forward three years to my daughter b being born.  She was two weeks earl bushe fine.  She has her PKU test and apparently her enzyme triggered them to do a DNA screening on her for cf (I had no idea that any of this had happened.). I got a call from the health department Thursday afternoon saying that she tested positive for one copy of a mutation.  I was told that two copies were needed for cf to be presented and for symptoms.  But I was still told I needed to take her for a sweat test to rule out cf.  I told them I was a carrier and my husband and I had both been screened so I was the only carrier but they are still suggesting this test.  This whole thing has freaked me out, as I have OCD so I've been worrying nonstop about it, even though the lady who called said she really doesn't think I need oher be worried.  I just don't understand why we still have to have a sweat test done if I know the mutated gene I have is the same one she has, and we know she only has one copy of it (mine).  I feel like I'm having to suffer through worry for something I was told wasn't possible.  Can anyone shed any light on this?  I understand there are possibly rare mutated genes, but my husband and I were checked for 136 mutations and 5 variants, and our daughter was checked for 139 mutations.  Any help or reassurance would be appreciated so much.  Thanks ladies!