I'm listed for transplant (actually top of the list), and am on Ativan (controlled substance) for anxiety. It's low dose, granted, but I started having panic attacks earlier this year due to some of my health issues and my CF doc put me on it right away. Since then we have weaned the dose down to only .5 mg every 12 hours (very low, most people take 1-2 mg every 6-8 hours), but that's all I need to make it work for me. When I started I would take .5-1mg every 6-8 hours and that got me through the worst of it until I felt I could start tapering down.
Although the meds were prescribed by my CF doc, my tx doc was/is on board. They were both concerned about making sure the dose was low enough that I wouldn't be walking around in a haze or something, but they also want to make sure that I'm able to live my life and do what I need to do to get ready for tx. When this first started happening, I was trying to suck it up but just really struggling. Actually my doctors all preferred the Ativan route to starting an SSRI/antidepressant therapy, which can also be used to treat mild anxiety, because there were fewer side effects, etc. It might have been different if I had needed a much higher dose or hadn't been able to wean down within a month or two of starting, but for me Ativan has worked perfectly.
I'm not sure if anxiety drugs are a different scenario than pain meds, and I know my doctors were more comfortable with Ativan than they were with something stronger, like Xanex or Valium. I do know of a couple of CFers who are on Valium or at least have a script for it and carry it with them just in case, and they're pre-tx. I also know of some post-tx CFers who are on these meds.
Is your friend having panic attacks with physical symptoms? I was getting things like racing and irregular heartbeat, difficulty swallowing, feelings of suffocation that led to hyperventilation, and other really classic signs of panic. So it wasn't like I had to convince my doctors there was a problem. Honestly I didn't want to be on drugs for anxiety (who would), and I "toughed it out" for like 3 weeks before it got so far beyond ridiculous that I absolutely HAD to do something about it. But if your friend is experiencing that sort of trauma then she deserves to get help -- ESPECIALLY if it's interfering with her ability to take care of herself or stay active pre-tx.
Could your friend make an appointment with a psychiatrist or psychologist to talk about her anxiety? These people are trained to deal with anxiety issues (some specialize in chronic illness) and could help her identify whether her anxiety would be best treated by drugs/meds or other options. She could then request that the psychiatrist contact her CF doc or give her a letter explaining the anxiety diagnosis and the recommended course of treatment. My guess is that this would go a long way toward convincing her CF doc, who is after all not trained to specifically deal with mental health issues.