Yeh I agree - it sounds like dropping hints is not going to work with this girl.. you might need to spell it out and tell her the reasons why you are not getting anything from the friendship and that you would rather leave it..
or just straight out tell her that you feel youve grown apart and you'd rather not catch up anymore.
I agree with Just Me about using the I messages... that way you get your point across about what you need rather than her feeling so much like she's being attacked. also what tashybabe said is a good way of going about it, but she will probably want some answers, so you might want to put them in an email or letter rather than getting into a discussion over the phone - she sounds like the manipulative type that could turn it all back on you.
Good luck!!