This comes up a lot, with CZ and with other guns.
Have your wife hold the gun with her hand on the slide (in a comfortable holding position), maybe at waist height, with the barrel pointed downward (in a safe direction). Then cock the hammer, and tell her to PUSH the frame downward with her strong hand, while holding the slide. (If you find another way to hold it, fine...) Putting the hand OVER the slide, in front of the sights, works for some folks.
The trick is to hold the slide still while PUSHING the FRAME. It's easier (and takes less hand strength) to just hold the slide still than to hold it while also trying to move it, too!
Cocking the hammer first makes it easier, still. Going to a slightly lighter recoil spring will also help, and if you've got a full-size CZ, it'll do fine with a recoil spring of 12 - 15 pounds. MOre than that, it's a chore for most folks.
Cocking the hammer first is the key -- and, of course, keeping the trigger finger OUT of the trigger guard area.