Man, you didn't make my "I want to help" list!

My wife is 68yo, and she would not be happy. Well, neither am I at 66yo.

Why not let her decide what she wants on her own? It has to fit HER, not you. The only way to find out is for her to try a lot of different bicycles in your price range.

There is NO WAY you can choose a bike for her. That could be a disaster. So much of choosing a bike is "fit" and that is not done 2nd hand.

Good luck.