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.
People need to experience something before they can ascertain if it is a viable option. Install Ubuntu or Linux Mint on a secondary device, let her see how familiar it is to her.
Then you can explain some of the other advantages of using Linux.
Seconding this! I’ve had the best success by using Linux to revive people’s old laptops that just couldn’t run other modern OSes fast enough, and if they’ve been impressed enough, they’ve ended up installing it on their other devices. Even if not (say, if it didn’t support some applications required for work, for example), they’ve usually at least kept it on said laptop.