Stem size in a Nishiki Riviera mixte?

[sarahspins]

Still trying to sort out brake levers and whether I should switch to an easier shifter setup.

There isn't much easier than stem shifters when you're talking friction shifting. I suppose you could try some cheap thumbies and see if she likes that better with whatever bar setup you end up with, since anything else would start to involve changing out components and get somewhat costly