Do NOT dump her unless you feel that you are wasting your time with her. Pot, like alcohol, can be a serious problem if the person refuses to stop being such a frequent user. Pot does not have the physical addiction side effects that alcohol/cigarettes/crack do but it does have a level of mental addictiveness.
For example, if she is smoking pot so frequently because she is avoiding a problem or issue that she does not want to deal with, then she does have a problem. But if she is smoking pot as a way to just enjoy her life then this is not a bad situation you are in. Either way, there are ways to reduce if not eliminate her need to ganja up.
I dated a girl who was a huge pothead. I mean, I have friends who chain smoke cigarettes, she chain smoked blunts. Now, she didn't do this to feel awesome and have a great time. She did this because she had a shitty childhood and was avoiding coming to terms with the bullshit she was dealt. After lengthy discussions, we were able to break through a lot of these issues to the point where it didn't matter if she was high or sober, she was still dealing with her problems regardless. So, it reached the point where smoking every 30 minutes was not helping so she stopped and become a much more active person (she would still smoke pot, but only on occasions).
Now, the tough one to get a girl/guy to get over is quiting the weed when they're doing it just to feel great and have a fun time (this was me). It wasn't hurting me at all though, I was still able to go to school and maintain a damn good job the entire time but what i hated about being on it so much was the fact that i did NOTHING when I was not dealing with responsibilities except smoke up. To get out of this mindset (and live a much more fulfilling life) I started traveling, going out.. experiencing things I hadn't before like sky diving and bowling (The dude abides). If you want her to quit smoking so much and she isn't suffering from any kind of mental stress then I suggest you take her out but to places where getting high would only distract her from where you are going (Anything active like paintball, sports, biking should do the trick).
Note: I am not a pot hater. I do ganja up from time to time when I am at a party. And I agree, pot is not a harmful drug that can kill you or make you a criminal. But, smoking it like its the only thing keeping you going is only going to demotivate you.
Edit: The only reason I'm giving this advice is because you sound like you want her to stop. If your cool with her smoking pot this regularly then more power to you both.