Thanks - last time I looked at npbackup it didn't support macOS! I'll have her give it a go.

Relica looks neat, but at that point I'd either suggest she uses one of the Borg tools or write a simple wrapper for her to trigger backups instead.

edit: Still looks a bit hairy for an average user to install currently, and the maintainer writes "I'm not planning on full macos support since I don't own any mac" - https://github.com/netinvent/npbackup/issues/28