OP: I wouldn't recommend telling her you won't allow yourself to be manipulated anymore, and to have a nice life / drop dead. All she will most likely do is play the victim card, act like she never had bad intentions and was being sincere, try to make you feel guilty and look like a jerk, and lure you right back in with more false promises. All while acting dumb and oblivious to everything she's doing. Much like how she "forgot", as it suited her. Selfish women like this will stop at nothing to get what they want, will turn things around on you, and they usually love the drama that comes with it. Most of them are quite crazy. They love the whole distance, game-playing, walking on eggshells, fighting, and other crap that comes with it. Drama queens, really. Doesn't matter if its friends or otherwise - they're still retarded, and set this crap up.
Manipulators and liars know what they have to do to get their way. She manipulated you into this, and will continue to do so when she senses you're moving on. Don't fall for it. Just stop talking to her. She might ask what your problem is, say you're being selfish and want all or nothing; you can't just be friends; blah blah. Also typical lines in these cases (when their interests are being threatened, and they can't USE you anymore). Don't even explain, or fight over this crap. She's not worth it; you don't need her, or to prove anything. She already showed how much of a "friend" she is.
This is why you don't become, or stay friends with women who do this. If you ever sense you're being used - get out. No, you're not a selfish jerk for not waiting around and being her doormat or back-up plan. This girl is using you, and you don't need people like that. Don't make it all about her - because that's what selfish people do best, as they play the victim all day long.
Don't explain ****, or get into a deep conversation about what's going on, and why you're doing this, and blah blah. She will never be honest with you. Just cut all ties, and forget about her. Don't fall for any flirting and attention seeking on her end, because its likely gonna happen when you fall away.