Just to reinforce in part what hokiefyd says, a few points.
Most modern flat-bar road bikes -- which appears to be what you are looking to buy or create (conversion) -- of decent quality are going to be well under 25 lbs or so in weight. The Fastroad is a good example. Some are much lighter than that.
Assuming your spouse likes the fit, going the stock route is going to be much more cost effective than converting a road bike -- if cost matters. Also, geometry will be optimized for flat bars.
I'd look hard at the offerings by Trek (FX series), Giant (Fastroad), and Canyon (Roadlite
https://www.canyon.com/en-us/hybrid-...ikes/roadlite/), if it were me. The latter especially sound like they might be precisely what you are looking for, but all three make excellent flat-bar road bikes.
Specialized, unfortunately, currently appears to have shrunk the Sirrus range (what I ride; I'm on my second), but I've attached a pic of mine (now down to 19.5 lbs with a few further replacement bits) just for interest. I'm a 'flat bar road-bike' guy; have been for years.