I don’t see why a good person couldn’t be corrupted in Mei’s route—so I still don’t see how being a good MC who turns to the dark side in her route would be a problem and about “revealing” herself, in what sense? It would make even less sense if she revealed herself to an evil MC, since they’d probably just kill her faster and without mercy. But like I said, I at least want to see how they explain removing Mei’s route just for being good without even giving me the option to choose.
As far as I know, the MC already knows she’s a snake, and she still stays with him for now even if he is good. The only explanation I could even remotely believe is if that goddess we saw in the good route interferes, or someone else does, and their paths get separated that way.