as we got off topic (ish) I can see the confusion-- we had mentioned the old 20-100 gear inches recommendation for touring, and a 100 g.i bike spins out at about 50k. My heavy duty touring bike has 103 or 104 g.i with 2in tires, and I spin it out at about 55k if I really spin gerbil fast on a downhill---which is ok by me, and I can still easily pedal at 40k or the very infrequent short times that one has either a long long gradual downhill or a super strong tailwind, but even then lets face it, you'll only hold this for a short time, whereas I can guarantee you that I've spent hours and hours and hours at 5, 6, 7, 8, 9, 10 kph climbing long Latin American hills--and exactly why I chose from experience to set that bike up with a 17-104 range.

as others have wisely said, somewhere in the 20 g.i range or higher if she really does carry a light load will work also, it really comes down to figuring this out from actual experience.
I do agree though that to me, its pointless having a high gear on a touring bike much higher than 110 or thereabouts, simply because panniers and crap are terrible for aero, bike is like a four mast schooner with sails , and unless you have a honking tailwind, I find it hard to get past 60, 70kph even though I would love to just hammer it.