FWIW, of all the bikes I have (one hybrid, two road, one touring and two mountain), I've only been able to test ride two of them. Of the remaining bikes, only one of them--the most expensive, a custom bike--didn't work out. In my opinion, if you have some sense of what kind of geometry your wife needs--and a good bike shop should be able to get a good ballpark for that--and the type of bike that best suits her, I wouldn't rule bikes that aren't normally in stock. Since your wife is short, even with the bigger brands, you might find it challenging to find bikes in stock for her to test.
But to your original question, I do think you're onto something with the Vaya. Of all the brands out there, I think Salsa offers the most variety of off-road bikes that might serve the variety of purposes she's looking for. The Warbird and Fargo would be especially attractive to me as a gravel bike. Velo, another member here, has the Warbird. She's given it high marks. If you work with a reputable shop, they should be able to address any sizing questions you might have. Kona is another company that has some interesting off road offerings.
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher