Create a normal user account for her instead of an admin account; though that means that you will have to install programs for her whenever she wants anything installed.
Also, buy her a decent security suite. I'm partial to Eset. Kaspersky is good too. Don't bother with Symantec or MacAfee.
Last, I recommend installing an ad blocker on her browser. The number of phone calls I got from my mother fell significantly after I installed an ad blocker on her browser. No more "this popup is telling me I have a virus" or "which download link do I click" phone calls. I recommend uBlock origin as it gets around most anti-adblock stuff. Still, some sites don't work well with ad blockers, especially streaming video sites (Hulu comes to mind), so you will have to make sure to whitelist any sites she visits frequently that won't work right with an ad blocker, or teach her how to whitelist them herself.