So off the original question, I think it's a little too vague.
This sounds like a home defense scenario. As such I would recommend something like a 20ga semi-auto shotgun or an AR/ak style of rifle with a sed dot sight.. once the safety is off all they have to do is put red on target. Maybe a light and laser instead, but you get the idea.
Handing a pistol to someone without them being overly familiar with them is not a good idea in most situations.
The only thing I can think of outside the home where firearms are used would involve my wife running away as fast as possible while I cover her. I don't think if I was to carry a back up gun it would go to her unless we were trapped in a room with no exit and barricaded in, in which case she would get whatever my back up is. Currently I don't carry one as I don't go anywhere too high risk, and my job doesn't carry any significant risk either.
A double action revolver with a weaker cartridge might be in order, whether it is 38 special or a 9mm with moon clips. Either one should be easy enough to handle, and moon clips can make reloads easier.
no matter what it is she'll need some sort of familiarization with it. I have a .40 laserlyte laser module I use with my glock. It seems more like a game than training when using it to shoot bad guys/zombies on the TV while doing dry fire practice, and gives some feedback on how your aim is. It's a little harder with a gun that doesn't have second strike capabilities, re racking the slide every shot gets tiring. Other than that it does help with some of the basics without the noise and smoke of the range (not that the smoke smells bad to most of us, but some people do complain).
As for a long/heavy trigger pull, you can easily swap in a NY-1 trigger spring to add a little more weight. You can even go to the NY-2, but that seems too much and even detrimental to me.
My wife started out on my ruger mk-II target pistol. Heavy bull barrel in .22 means almost no felt recoil and little muzzle blast. Her first gun of her own was a mossberg 500C shotgun (20 gauge) as it's light enough for her to hold (under 6 lbs) and small enough for her frame (she's from the philippines). After that I had her buy an AR-15 as she wanted a rifle. She loves her AR-15 and shoots it whenever she can get me to take her out to the range. Little recoil, not that heavy, adjustable stock, and relatively simple controls make it her go-to gun if she needs a weapon at home. The most recent gun for her is finally a handgun. She now has a walther CCP. controls are simple, it's a striker fired with a relatively small external safety that's easy to turn off with your thumb, comfortable in the hand, 9mm. Due to the design it's easier to rack than most semi-auto pistols. Downsides are 8 round magazines even though the grip is big enough to allow for more, and that it's a little finicky so far on ammo it will feed reliably. being able to rack the slide easily was one of the main requirements.
an ar-15 pistol with a sig brace might also be in order, it's sort of a compromise between all of the things I mentioned earlier, and possibly do it in something like .300blk. easy to control, easy to point and shoot, large capacity, add a red dot sight and maybe a light to it and you're all good.
On the other hand you can't get much more simple than a good old double barrel shotgun.