Most Helpful Girl
Well, then you're going to have to warn her that enough is enough. Stop being nice to her and start ignoring her after you tell her what's going to be if she doesn't stop. The question is, is this your ex, or girlfriend, or friend? If girlfriend, you need to be the one to break up, it will be her problem if she doesn't realize it's over. If ex, you don't owe her an explanation, just carry on as usual. If a friend, then like an ex, you are not interested anymore. But overall, regardless what she is to you. If she doesn't respect your boundaries, other people of authority will have no choice to forcefully implement them, or you may have to change your job. Which you really shouldn't have to do over a girl.
Most Helpful Guy
Hurt her. Do whatever it takes to be able to. Tell yourself whatever will enable you to pull that trigger. Hell, she deserves it. You know she's fucked over at least one man who didn't deserve it, you're just the agent of karma. You don't want her any more, so who gives a fuck about her feelings?