

Initially, the player is blocked from entering the second Large Room by Marguerit Maida's pet Snow Stalker laying in front of the door. There's also a Reaper Leviathan skull hung on a wall. The first Large Room contains a built Seatruck Perimeter Defense Upgrade, a Snowfox Fragment and the Test Override Module Fragment. Entry to the base is via a Bulkhead that separates the Moonpool from the base's interior, and it will be open after the player encounters Marguerit Maida at Delta Island. The structure overall has a grimy and dishevelled exterior, and a dark and cluttered interior filled with hunting trophies, personal effects and partially dismantled equipment. So I think it was the combination of the cold, prolonged exposure which caused a partial immunity(like a vaccine), and the struggle of the spread of the disease kept her alive so long.The base consists of two interconnected Large Rooms, one with a Glass Dome roof, and a Moonpool containing Marguerit Maida's Prawn Suit connected by a right-angle section of corridor. I doubt many infected creatures got past the ghost leviathans. Also, if the disease escape in the creator after the architects had it, then it would take a long while for the disease to spread. She may have even been showing signs of infection recently and she probably got the cure when the rest of the planet got it. Also, the disease probably infected Marguite but since she was on the planet so long it was slowly infecting her. Also, I saw something in the comments about the architects being more advanced then Marguite(however you spell it) yet these also are unaware of simple things, such as dreams, or even asking an intelligent creature for permission to use her eggs to save countless lives.

The disease is very strong but even the strongest diseases can't spread in some situations. The disease persisted on the leviathan all this time and even after parts of it was unfrozen. Also if you have reached a certain point in Below Zero, the frozen leviathan didn't die of the disease and froze to "death". Colder climates typically slow down viruses and diseases so that could be a factor. She probably floated to the colder regions while floating on the reaper.
