I'm not going to let my girlfriend pop her pimples.
Why would you even deal with popping her pimples? Is she making you watch her?
No, but she needs to stop doing it.
Your intentions might be for a good reason, but it's her body. Unfortunately you can't stop her, even if you think it's a bad habit.
I'm going tell her to stop anyway.
Well, if you think that stopping is good for her then you can do so, but you can't force her to stop as it is her body, and you can only guide her to do what you think is best for her. If you do something she doesn't like, you won't want to be forced to stop, right?