It doesn’t have to be 1:1. Make sure to install drivers, set up proton (so that proton is used by default), Install Only Office (because it is the most appealing to Microsoft office user) and if she really needs it create web apps for Microssoft Office and ensure that they can be launched from the desktop, taskbar, and start menu. Also Install adblockers and whatnot on her browser. Just nothing that could interfere with her workflow. So Ublock, Sponsorblock, CleanURL, I Don’t Care About Cookies, and Return Dislikes to Youtube. Also use this hardening script because it makes Firefox secureoit of the box and in my experience has never gotten in my way: github.com/hnhx/user.js
I guess theming would make a lot of the work, I don’t remember the names but there are a few plasma themes that aim to mimic windows 10 and 11. If not the entire theme, the icons at least would make it way more intuitive.
For the office suite you might want to check out OnlyOffice(or even freeoffice), it probably looks more modern and less jarring than libreoffice for someone coming from recent versions of MS Office.
The start menu also has versions of it more similar to the windows one, but the standard one Is much better, maybe it’s a change she can get used to.
Make sure the desktop is in Folder View, so she can put files and folders on it, and set Dolphin’s view to the one she’s used to, icons or details.
I’m not sure for gaming, but maybe check beforehand if hers work on kubuntu.
Finally I’d make a post-it explaining the names of programs: dolphin - > file explorer, Kate - > notepad, ark - > 7zip and so on. The most frustrating thing is looking for a program that should have an obvious name and finding only unknown nicknames, it takes a while to get used to!
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