Carbon steel is a big :thumbup:. That opens up a lot of very simple possibilities.
I've gotten into the habit of 'stropping' my carbon-bladed (1095) Schrade 8OT stockman to keep it in shape, which also includes using wet/dry sandpaper over my strop block. Some 400 or 600 grit is great for forming a new edge on pocketknife-sized carbon steel blades. It can easily be touched up after that, with just a handful of passes on the same or higher grit. As for stropping, chromium oxide (green) compound on leather works great, as does silicon carbide (black) or even some 1 micron diamond paste. The green compound is usually ~ 0.5 - 1 micron particle size, and the black compound I use is ~ 1 - 3 micron. With carbon steel, since it abrades easily and takes a very fine edge, I always prefer to keep the stropping compound's particle size small. For sheer simplicity and availability, I think green compound is a no-brainer. The others can be purchased and experimented with at your leisure, if you wish. Here's a pic of the type of strop block I use, with some sandpaper wrapped around it:
The block is made from some red oak stock (2-1/2" wide x 1/2" thick), picked up at the home improvement center. This could obviously be done with much simpler wood; lots of options there. I used some 2-1/2" wide carpet tape to attach the veg-tanned leather to the wood. That's quick & easy, and mess-free. Many use contact cement or other glues to attach the leather, all of which should work fine. The sandpaper is wet/dry type (3M or Norton brands are very good), and grits up to ~ 600 or so can also usually be found at the home improvement center (also where I bought the carpet tape, BTW).
I also have a 1-1/2" wide x 1/4" thick version built from the same/similar materials, which is all the more 'pocketable'.
My point in showing this is to emphasize how simply & inexpensively this knife can be maintained. Obviously, there are many, many options out there. But, if you'd like to keep things simple, as well as indoctrinate your daughter to a real skill (freehand stropping and sharpening), I think the example above is a easy way to start. I'm confident you already have the stropping technique down, based on your post. So, I think passing that skill on to your daughter might be a natural. The technique is exactly the same, with the sandpaper or without. I really wish I'd learned this method when I was her age.
Forgot to add, you can also use the sandpaper directly on top of bare wood. Same stropping technique, but the firmer backing reduces the chances of rounding off the edge. I usually start this way, when re-forming an edge on the sandpaper, then I'll flip the paper to the leather side as the edge becomes more refined. Use a conservatively low angle and light pressure on the leather side.