Linux is not all gloom-and-doom. There's multiple ultra-light distros out there such as Mint, or even Puppy Linux. Your job is to sit down, talk with your wife, figure out exactly how she uses a PC and what she wants, and figure out if Linux can deliver that experience. Most any Linux distro can as long as she doesn't insist upon using software that is only available on Windows.
I'm gonna bet Kubuntu, Manjaro, and Mint will do nicely. There's no need to teach her the command line. You just need to set up the system for her. I, for example, have Manjaro running on a low-end ARM processor with only 4 GB RAM. It is slow to boot, but after that, it does fine as far as the basics - browsing, email, office\productivity, etc - as long as I don't get stupid and try to keep 10 apps open with Firefox open with 20 tabs.
This is a two-part problem. You figuring out exactly what she wants and then taking the time to ensure Linux is configured to deliver it.