My mom has a business and mostly uses Windows and Mac OS X; I mentioned Linux because it could help save money.
She is unfamiliar with Linux though; I gave her some basic introduction (uncertain if it’s any good, but sure), but I would like to be able to ease her into Linux if she prefers it.
I recommend Trisquel. Use plasma DE for sure, it provides amazing user experience. Tell her to not expect things exactly like those of Windows or Mac and learn till she becomes comfortable. Initially she’ll struggle, later she won’t even think of using Windows or Mac.
This is assuming her computer can run without any proprietary drivers. Trisquel uses the Linux-libre kernel, so some stuff like WiFi may not work. But if it’s just a desktop workstation that connects to Ethernet, she should have no problem.