Smallish caliber pistol

Get revolvers out of your head, a small revolver shoots nothing like a cowboy action revolver. A modern .380/9mm semi auto pistol plus training is the way to go.

I would personally not let YOU or the salesman give her any leaning to what pistol to get. Let her hold a bunch and pick out what she likes. When you get it narrowed down let her go shoot them.

Best thing that can happen is for her to pick it out and like it.

Whatever she is comfortable with

Smallish caliber. No. Revolver, 38 short barrel is easy but Glock 43 9mm is better.

Did this a few years back with my wife, also a school teacher. The Smith and Wesson 380 M&P Shield EZ is something she can operate, has the handle grip safety, as well. Very accurate shooting at the range. comfortable in her hand, easy to rack ammo, and large enough capacity magazine to handle misses if nervous having to protect herself.

It sucks that she is so clumsy and lost it while boating.

Sig P238 (.380) is a great little pistol - but getting a bit harder to find, especially since Sig came out with the 320 in .380.

I'm a firearm instructor and have been teaching for nearly a decade. Every female in my classes starts on a full sized 9mm. The fan favorites are my wife's HK VP9 and my S&W M&P9c 2.0. They have slim grips but still have all the attributes of a full sized gun. I'll quote a post I made/bookmarked about 7 years ago.

https://www.tigerdroppings.com/rant/display.aspx?sp=58237860&s=2&p=58233872#58237860

Won't post the whole thing here but full sized 9mm for ANY new shooter - period. There is no advantage to making a gun smaller other than something you plan to conceal on your body. Your wife should be using an overhand grip to rack the gun (thumb pointed in her chest, slide pinched between base of palm and fingertips) anyway and she will utilize large muscle groups instead of small ones to work the slide. A full sized gun will have a lighter and longer recoil spring that will make it easier.

Like many have said here, don't let anyone else tell her what to get or not get (Including revolvers)

The best personal defense firearm for her is going to be the one she's comfortable with and the one she's willing to train with routinely.

The first thing she should do is think about what her expectations will be for needing this firearm.

Personal defense is a broad category. What are her expectations for needing it and as much as we would like to prepare for every possible situation we can't in our normal civilian lives.

I'm not a teacher but perhaps if I were I would be thinking along the line of being the last line of defense for myself and my students. What that would look like to me might be to stay in the class in a close quarters area with limited access to get in to us so I could focus my attention (fire power) to maybe that one point, increasing my shot/hit ratio. Probably not out roaming the halls on offense where threats may come at longer distance and from one of multiple directions. I would likely want something with as high of a caliber as I could accurately engage a threat out to a max of 20 feet or so. Personally I would feel comfortable with my Ruger Sp101 .357 and 1 extra speed loader in that situation, but that me with my experience and training. Definitely not what everyone would be comfortable with.

And while she's thinking about type and caliber of firearm it's a good idea to think about every conceivable problem that could arise with that firearm. (Shooting as many different types as possible is the best way to not only decide if that type is right for you but it opens your eyes to possible problems that you may not have other wise considered if you didn't have a chance to handle it. For me the SP101 offers more than enough stopping power and greatly reduced possibility for malfunction in the scenario above, but again that just me.

Anyway good luck and don't rush the decision, If she ends up getting something she's not comfortable with she's not going to train properly with it then it wont matter what type and caliber she has.