There is no much point trying to find a specific meaning or direct match with an English word for these adverbs.

Ne and pas are used in negative statements, either alone or combined.

You translation of elle ne va plus au lycée depuis… by "she not going more to the high school" is weird. I’d rather expect: "she hasn’t gone to the high school for…"

Anyway, formal French generally uses a split negative ne + another adverb like pas while spoken/casual French often drops the ne : elle va plus au lycée depuis…

See also:

Quelle-est-la-différence-entre-ne-ne-pas-et-pas

What is the construction used in negating with "ne pas" (but not ne..pas)?

Ne pas, ne point, ne goutte

Why does French use a "split negative"?