She's seeing how far she can change and control you.
If you quit for her, things will only get worse and she will desire you to do this, that, and just about everything for her. That's my 2 cents, tell her to fuck right off and that she shouldn't have got with you in the first place knowing full well you smoke cannabis if she didn't like it.
Although I did read a success story about a guy giving up pot for his lady, so it could work out for you...