Must respectfully disagree with Linux/Chrome suggestions. This lady already has a capable Windows pc according to the op.
She has at least some familiarity with it and with the addition of Teamviewer and the OP's support she should get along fine with what she has.
Don't get me wrong, I use Linux Mint and have used Ubuntu and like them both. But without support neither of them are for the faint of heart or for someone who isn't willing and able to learn some basics and get familiar with a new interface, new terminology etc.
As you well know, just installing a printer driver can be a challenge.
The idea that a Linux Distro is immune to viruses and malware is a mistaken one. A Linux distro CAN become infected, mostly with Windows viruses but they can't run on a Linux machine, but they CAN infect another Windows machine! So, the OP logs into Teamviewer with his Windows machine and he's infected.
I've installed Linux Mint on a couple of Windows XP computers for friends who didn't want to pay for a modern copy of Windows and didn't want to buy a new computer. One couple, in their fifties, loved it and continue to use it, another person, younger, ended up selling their old pc and bought a new one with Windows 8.1 preloaded.
I would definitely not recommend Linux for this situation.
Larry