Agree that except for people with fairly serious injuries (or limits for surgical recovery), arthritis (hand grip strength esp) or similar, everyone can rack a slide.
Many people IME do NOT and have to be assured that they cannot break the gun, or injure themselves. Even people used to mechanical objects do not typically manipulate a tool like this. You may pull with a wrench or hit with a hammer but you use the tool ON something else, you don't use force on the tool itself, if you follow.
So, that's step one to me. Try to assure of confidence in pulling the gun HARD. Barricade cocking is both a useful technique, and good intro to the force required. (WITH DUMMY ROUNDS!!!!!) put the rear sight or some other easy to index part on a rigid thing like the edge of a counter or table, and push with the firing hand until the slide is all the way to the rear. Do note: not the kitchen counter
The gun will scratch stuff up, so outside or in the shop or something.
The second failure most people have is — as stated above — riding the slide forward. Even a little bit of lowering the slide will reduce the slide velocity. You have to make sure she's pulling ALL the way to the rear then just letting go. Same issue as the first of mindset, confidence. That the gun won't break in half, the slide won't fly off, etc. I am super opposed to using the slide stop lever as a slide release (whole separate topic, but let's skip it for now) but a good exercise then is:
Insert an empty mag. Have her pull or barricade cock until the slide is locked to the rear. Change magazines (again, for a loaded With Dummies one) then have her push the slide stop to let it fly forward. After a while (not just iterations, but maybe days) then have her pull and release off a "loaded" magazine and see how it goes.
All this also is why a lot start with sub-calibers. Train on .22 as it's stout enough to get used to the mechanicals without so much effort, so stepping up to centerfire is a little easier then.
I'd say also, if willing; take a video of her manipulation. We can see a lot in a video, suggest specific issues or fixes. But likely the things Tilos et al shared are what would be suggested, so try yourself to look close at what she's doing, and compare to proper techniques.
Yes, the EZ is a great gun, also, if you want to sidestep the issue.