Sorry - took a while to reply. University-level teaching requires at least a Masters level or equivalent qualification. That's because such positions are more-or-less a buyers market, and the buyers want their applicants to be as well qualified as they can (looks good in the university handbook!). A doctorate is fine too, bit overkill for a first academic position - secure it whilst working. Post-doc is just pure research and publishing - you need to have sponsorship or a steady income to feed yourself.
You're right to always think onwards and upwards. You only ever do a Bachelor's once - unless you're just studying for the sake of it.
But if your friend is content to live in Australia why not try and find a means for her to continue doing so. I can almost guarantee post-graduate study there is far more enjoyable than in Japan.