I had a 20 inch frame and although I'm 6 2 it was huge. The top tube length (in 1995) was very stretched and they didn't do dropped top tubes to increase standover. I suspect (with hindsight) that I'd have gotten away with an 18 inch frame with long (ish) seatpost and mid length stem. I think that even a 16 inch frame would be big for your spouse. You could email Pace direct and ask about the sizing as they used to be pretty good about retro queries.