What style is the bike? I think her ride position will make a big difference. The more upright, the easier gear she'll need. Way up, heavy frame ... 38-19. Down toward a drop position a much harder gear is easy to push.

I'm just starting out and have bad knees so I'm going 44-20 (flatland here). I ride quite a bit and do like to spin. I still have the freewheel & cog and 44-22 is sweet, but I think I want just a bit more for moving along.

Good Luck and just make it clear to her that it is something you can change.