I missed the news for a few days: when did Hell actually freeze over?

Sorry; I have no really useful information to add, but I couldn't resist asking the obvious question. It would seem that high-quality down would be part of the answer (say, something by Western Mountaineering or equivalent quality) - assuming that she is going to be able to keep it reasonably dry where she is going. (If she can't keep down dry, the next logical question is, will she be able to keep synthetic insulation dry in those conditions? "Warm when wet" might hold somewhat true in the eastern U.S. forests in above-zero temperatures, but I can't imagine it making much difference at 40 below.)

Good luck helping her find something that will work.