Here's my $0.02 humble opinion.
While any properly chalked tip can put sufficient spin on the CB, there is a thing called spin to speed ratio. A hard tip puts its force on the ball for a shorter time than a soft tip if the force is equal.
It is easier to put more spin to speed on a cue ball with a softer tip than a hard one given the same stroke. Note I said stroke not force & keep in mind that I am not talking about spin alone but spin to speed ratio.
That being said, if one maxed out their cue speed say like on a break shot the hard tip would probably put more spin on the CB but with more speed attached to it than the softer tip.
It is similiar IMHO to the string tension of a tennis racket. With a soft strung racket the ball stays on the strings longer than a tightly strung racket and therefore can put more spin on a tennis ball than a tightly strung racket with the exact same stroke.
Golf shafts are simliar in getting the most force out of a certain speed swing.
Golf club shafts & tennis string tension are fitted to the player. Why not cue tips.
I have been using very soft Elk Masters & Brunswick Blue Diamonds for 46 years & now have a Kamui SS.
The reason is that I feel I can always add CB speed when I want it but getting a high spin to 'slow' speed is a bit more difficult to get & the soft tip makes that easier IMHO.
So, as to the tip for the wife, I think it woud depend on her stroke. Is she a Jean Baluka type or a 4'10" type. Can she add power when she needs or wants. A medium tip might be the way to go if one is not sure just what one wants or needs. From there a modification can be made.
I hope this helps & do not have any high speed video to support my opinions, just 46 years of playing time.