She's trying out cycling as a replacement for jogging, which has been too stressful for her joints, so I think this will be more than just the typical roaming the neighborhood that I did at that age. Still, 1x isn't a bad idea.
The tires that are on there now are labeled as 25s but measure 23. I might need to dimple the chainstays to make 28s fit. 650B with 28s would make a lot of sense for this bike. If I could find a reasonable set of used wheels, I might splurge for 650x28 Conti GP 50000s.