Just tell her. What's the point of going through all that when you could just tell her and not worry. You never know, she might let you smoke it in your room.

Smoking in a bathroom is not fun, it's for pissing and shitting, not smoking weed.

Parents are meant to be the ones you can tell everything to, their meant to love you unconditionally, so just tell em "I smoke weed, fuck yeah. Long live weed" And there you go. They know, and you havnt got to smoke weed in a toilet.