She grows bigger and smaller and so on and so forth. This is supposed to represent her addiction

I don't think this represented addiction, I think it represented changing perspective of reality. Mushrooms seriously distort your depth perception
and perception of sizes and such.
The Cheshire Cat didn't really come out someone telling her to stop in my mind. I haven't seen the movie in awhile, lol, if only you knew what i
was doing the last time i saw it, so I'm not sure what the cheshire cat could be.