Personally, I wouldn't recommend Arch (even the "friendly" variants like Antergos) to the less technically inclined. You don't need a to be extremely familiar with Linux to get started with Arch, but you do need to be comfortable at the command line and are expected to be able to read the (excellent) docs and debug things yourself.

It's a very educational experience, but not really something the "average grandmother" is likely to have the patience for, particularly when they're just trying to watch a flash video on Facebook. That's the real strength of Mint, and I'm not sure what best fills that niche if Mint is off the table.