When she needs support or assistance, that theory holds about as much water as a fishnet.
It's much easier to diagnose + make changes to remedy the problem on Linux (if you know your way around).
Hell, even if you don't: the majority of the system (barring systemd) is fairly transparent, and you can readily find documentation/articles/blogs to better help you understand the problem -- and even fix it. Contrast this to Windows: I have no fucking clue how all the moving pieces come together. I just know that I can fuss about deep in settings/group policy/on the command line and roll the dice to see if any improvements are found.
Granted, most of the time it is the same for Linux, but it's much easier to simply SSH in, muck about, and so on, than it is to use TeamViewer (or go through the logistics headache of actually getting in front of the machine in question).
PS: real case from a few months ago on Fedora.
PPS: oh, and guess what advice I got from the "helpful" widely advertised Linux community? "You have picked a bad distro and DE combo" (c) and "You have incorrect hw env for these distro and DE, why didn't you pick ubuntu/mate?" (c)
For me Linux will probably never be "home ready" and will stay on servers and embeds where it is perfect and amazing.
Ha! At one time I cursed those who threw this at me; now I know better, and throw it at others!
All joking aside, I really dislike Fedora and Gnome. It does have a lot of problems.
But, onto your problem: I would start at looking at the xserver logs, and ask about any recently changed settings/configs/options or updates/rollbacks. The logs are usually fairly good at telling you if something is !!!WRONG!!!.
Those are usually the most likely culprits, if the DE was working fine until all of a sudden it didn't anymore.
If it's a fresh install and right-off-the-bat it's buggy, then it's probably a HW issue (or the distro is terribad).
I would try xforwarding, and other built-in remote desktop options, to see if I could tinker around and get real-time feedback on how the display was looking.
On the other hand, if it's Wayland: I must yield, bow my head, wish you well, and withdraw from such an exercise.
Dude, I do this. I literally onboard a good amount of friends and family to Linux. Also occasionally help out Mac people as well. Even now, I hear from the Apple people more.
I don't know why you want this to not be true, but, sorry, it just is. Once set up, Linux is MUCH MORE SOLID, much more "set it and forget it" than Windows or Macs. I'd agree that, say, 5 years ago, the set-up was harder. But that's no longer even an issue. I install Xubuntu on the thing, tell them their password, tell them to go ahead and click yes when it's update time and I just don't hear from them all that much ever again.
Another switch in 2019 (Unity->KDE) I can't tell if it got even easier, because I was not as much of a noob anymore than 2 years ago, naturally.
If anything the most likely person to have issues and break Linux is the kind of person Linus is: an experienced Windows power user.
The vast majority of people use their PCs like (overly complex) tools while having an at-best superficial understanding of concepts like what files and folders are. By the moment someone realizes something like a folder being nothing more than a file with a list of other files (instead of something handwavy magical that groups files together), they're already above the 0.1% of the PC using population.