Yep, it's quite likely a "fix the shooter" issue, not a "fix the gun" issue.
One thing that might help is to install Hogue grips. That will soften the already mild recoil of the 3913 a bit more, and the added grip girth might help with their grasp of the grip frame.
Locking their wrist is still up to them. Their wrists should be straight & locked behind their grip, not "bent" either side-to-side or up & down.
The frame must be held sufficiently stable so the slide can cycle at its intended speed, which is critical to feeding "timing" during the recoil cycle.
If you've had the gun for more than 5 years, or have fired 3-5K rounds, I'd also consider replacing the recoil spring with a new factory spring, myself. (The factory recommendation is 5K rounds, but I tend to err on the more conservative side with my own 3913. Of course, I shoot issued +P & +P+ ammo, too. )