How do I lock down a non-geeks MacBook My mother in law is techphobic. She also lives 8000 miles and several time zones away. So I want to help set up her computer as solidly as possible without needed much long distance sketch support. 

I'm updating her Mac to macOS Sierra. I cleaned off mackeeper. I have her use Google Chrome for anything Flash related (yeah I know, but she watches videos and the ones she likes need Flash). I was thinking of restricting apps to App Store apps, but wonder if I'll need to support that long term. 

She's based in Taipei.  No current Apple stores. She hates asking for help. I'm pretty much the only one she'll ask. She has backups (not sure how current). And horrible password discipline (currently her account doesn't have one - I had to add one just so I could do sudo in a Terminal)

Any other tips?  Thanks.
Some things I would look into in such a scenario:

Backup

Absolutely essential, and something you can set up easily. At least attach an external drive and configure TimeMachine. If you want to add more protection against handling errors or such, use a service like Backblaze or Arq to get an off-site backup.

Remote Access

Sooner or later you will do support over phone and it is much faster and easier to do if you can see what is happening on the screen. I usually use Teamviewer which is easy to setup and use. Just make sure that everything is working as it should before you leave house.

Restricting things on the computer itself

With remote access in place you can get rather restrictive with what the user can do. You probably don't want to give them administrator rights (so make sure you set up a non-admin account for them) which eliminates most handling risks. I would also restrict application installation to the App Store.