Hello. Make sure your daughter is seeing a doctor that is familiar with CF and or affliated/accredited with/to a CF center.
I was told there are over 1500 mutations, with more being discovered every day. I would give the sweat test another go (at an accredited center).
Did your daughter have a fecal fat/elastase test done yet?
Hang in there and hope you get some answers soon, It is very frustrating not knowing what is wrong with your child.