Thanks, it was actually considerably easy because it's exactly how I feel. The only reason for messaging her back is because the message she sent me makes it look like she's still in control, she seems to believe that she can just message me whenever she wants in the future and I'll be okay with that, when in fact, I won't. I guess my original message to her was an ultimatum. Either she doesn't want to speak to me, and then I'll just remove her from facebook etc, or she does want to chat and will make more of an effort to not jerk me around.
The fact is, after that reply, it's quite clear that she doesn't give a damn, so what's the point hanging round in hope that she might contact me in the future only to be the exact same way with me? In my mind, I want to send her a last message telling her not to bother and then I'll just block/delete her so that she can't contact me again.
It seems a bit silly to get back in touch later whenever she wants to because then my whole message will become what Giga said, just another time were there are no consequences for her actions.