You may be overthinking this.

What kind of a bike does your wife have?

If you've actually put a few miles on your road bike, and your wife hasn't, you may be a stronger rider than she is. In that case, no sense in going out and spending a fortune on your dream bike while she rides a beater.

Plenty of MTBs and Hybrids on Craigslist and at thrift stores for around $100 or less.

Get out on the trails, then see what you think.

Suggestions for cross bikes are good. They occasionally show up on Craigslist depending on the size of your market.