Flash it for her. The result will be a more stable (in terms of not shitting the bed randomly one day or changing the entire UI) and decluttered portal to whatever website she uses it for.
"You moved my Chrome. I liked my Chrome. Put it back. I can't get to the Facebook. I want to talk on the Facebook and I can't because you moved my Chrome."
Someone who is 75 years old today was 49 years old at the peak of the dotcom craze, and is probably a lot more computer literate than you're giving them credit for. What you're saying might have been true 20 years ago, but it isn't today.
If you talking of users who dont install their own software and just use browser only then Linux was better for them for decade.
Now you can even install something with read-only system partition with snapshots so not even a power outage can corrupt anything.
For non-power users who do need to install something it was never perfect, but now these immutable distributions are here. They have their own downsides though.
Guessing this is just a hypothetical, but if you really can do that (disable the DM via the GUI by accident), I'd be curious. If you told me to do that on purpose, my first instinct would be to uninstall the package.
If you do have permissions to install packages you can end up with a system in messed up state pretty easily.
1 - Enable wrong ROMFusion because you need these damn video codecs for VLC. I have like 20 years of Linux experience and I still messe up Fedora in 2025 trying to make video work.
2 - Just forget that big update going in background and shutdown system when not appropriate. Boom. On Windows its just much harder to accidentally do it.
Only solution is really distros with immutable root and snapshots.