What Should I Do About My Mother?

[Caroline]

I don't know much about Twitter but can't you block her or something?
As for the rest, presumably you are 18 and an adult. Since she's not paying anything towards your schooling she has no way to threaten you so I imagine that's why she playing this game.
Sounds like she's kinda nuts, to be honest. Smoking weed now and then won't kill anyone and shoot, if colleges kicked out everyone who tried it, they'd be scrambling for students.
With people like that, I've found it makes a difference if you act the way they do. So, stop being polite, stop being nice, just treat her like you would any other annoying crazy person.