Training. Most full size pistols can be racked with proper technique. Yes there are folks who can't operate a slide for one reason or another. Then the proper pistol will be a factor.
Keep in mind, generally the shorter the slide, the stiffer the spring. So a 3" semi auto in 9mm will be more difficult than say the same gun with a 4" barrel.
As to the easier to rack pistols, there are a few.
Smith & Wesson Shield EZ in 380 or 9mm. These were designed exactly for this.
A full size 1911 in 9mm. These are super easy to rack. And if you get an all steel one, recoil is super light. Although keeping a 45 oz pistol held up on target for any length of time can be challenging for some people lacking upper body strength.
Any DA/SA pistol with an exposed hammer can be easier to rack if the hammer is cocked manually first. Beretta 92, 3rd Gen Smith, Sig 22ish series, CZ 75 are a few I can think of.
If it's just for range run and practice, the larger 22lr pistols are very easy to operate. The M&P full size and compact, Taurus TX22 and the Ruger SR 22 come to mind.
But training should be done first as with proper technique, it opens the door to a greater number of options.
My mother has been happy with a M&P Shield EZ 9mm. Some youtube reviews say it measured about 1/2 the effort to operate. Slide is also shaped at the rear to better grasp along with a magazine that is easy to load.