My daughter has CF. She took periactin for a short time. It made her horribly emotional and she didn't gain much weight while on it, so we stopped.
You say she is a carrier, did they only find one mutation on the genetic test? There are about 1,500 known mutations, and more being discovered. The basic genetic test only covers the most common mutations, so it's possible that a person will have a mutation that isn't commonly tested for so it looks like they only have one mutation.
I myself was recently diagnosed with "atypical CF" after a lifetime of asthma problems, repeated bouts with bronchitis, pneumonia, aspergillis (in my lungs), and pseudomonas in my sinuses. I don't have the typical digestion issues of CF, though. All of my kid's have had genetic tests but I haven't because my insurance won't pay for it.
Does your dd excrete a lot of salt in her sweat? That's how I knew our dd had it even before the tests came back. She tasted like a salt lick! Sometimes if she sweats really badly you can see salt crystals form on her skin.
As for the enzymes, my dd did well on Pancrecarb. They took it off the market since it didn't get approved by the FDA and now she is on Creon. She had Creon once before when she was a baby and it didn't do a thing for her. We will see if she has gained weight on it at her next appointment. If not we may try Zen-pep. Also, how do you dose the enzymes? They really only work at their "peak" for about 20 minutes (so I've read and been told). If your dd is a slow eater it may help to break up the dose. My dd takes 4 with meals and we usually give her 2 at the start of the meal and 2 halfway through so the effect lasts a little longer. Most enzymes work better if the patient is also on a reflux med (Nexium, Zantac, etc) because too much stomach acid can cause the enzymes to be dissolved before they reach where they need to go to help with digestion.