you know...
...you've always known. The moment you suspect it you are correct. Be confident in what you know and ignore your mother's other enablers. You are intelligent, and you are seeing what you think you're seeing, smelling what you think you're smelling, and trying to think anything else is textbook denial.
If they have Al-Anon in New Zealand find yourself a meeting and go.
Good luck and God Bless...
Cyranoak