From now on AMs are lucky.

It's not 100%, but that does work.

You have to clear the spawn queue to get MM. She only spawns after the Fairies. So if you kill some pigs and the Fairies appear, kill the fairies, and MM will be next if it's time for it to spawn.

What Kevvl said ^^
It's a myth, that makes sense, but doesn't really "work." Only coincidentally works. MM spawns after 45mins. Nothing more, nothing less (Well, maybe, give or take a bit.) It uses logic, but isn't true.