I use an IOGear KVM, and experienced incompatibility using off-brand wireless mouse and keyboards.
(I think they mention this possibility on their website.)

The strange thing is that the scroll wheel on an old Logitech would go haywire on that, but it works fine on the laptop.

Her mouse is wired, just has to go thru the hub, which I didn't have connected correctly at first.
All seems fine now.
Of course, it's taking too long to down load files to the USB stick for transfer to the new computer, but hey, I don't have a problem with it.

Plug the Win 7 machine back into the network and set up file/printer sharing.

id10t - that is next step. She's now transferring the files she wants. I'll look into doing the file/printer sharing after she's done but I'd really rather not have both computers talking to each other.

Ah. Well, to have computers connected but segregated and still having a common spot to put files is possible.

Either you need high level geek skills and something like a Raspberry Pi and a extra USB ethernet for it or you need to buy the right hardware. There are home/small office routers that have firmware that make having multiple subnets easy and not talk to each other but can access the world or other designated subnets.

You need 3 subnets. Subnet A is what you have now with Win10 and whatever else. Subnet B is the old Win 7 machine. Subnet C is the way out to the world and where a file/print service lives (via a NAS or just printer configuration). Subnet A can see itself and C and the path to the world. B can see itself and a path to the world. C doesn't need to initiate any connections into A or B so it just needs to see the world. You could even limit the B subnet to ONLY seeing the C and not having internet access.

That is the dichotomy of personal privacy data:
It has to be permanent and absolute and with no external connections.
(but that is simply not possible these days)

Intel supposedly makes a CPU chipset which is self-powered and has integrated wireless functionality. Even when "off".

Data transfer is always possible through the power source i.e. house current on different frequencies.
That might become the future of ISP.

There is "air gap" technology which transfers from speaker-to-speaker.
(remember that remote audio spying has long been capable of picking up deflections off a window pane)

Regardless: Stay paranoid.
Only stupid criminals don't advance and get caught.

You could move the storage device between pc's, connect them to a hub or switch and copy files over the network or use a usb stick. Connect the 2 pcs to the network, unplug your internet connection then setup file sharing. Copy files, disco the old pc then plug in the internet connection again. Or use a usb stick.

good job getting it together, this kind of thing can be confusing