Well, I would just let her know how you feel and how you felt used.....basically tell her the truth of the matter. Let her know you need time to process your feelings and that you aren't going to meet with her at this time.
How long have you been friends?
Sometimes relationships come to a fork in the road and you have to decide is it in your best interest or not.
Hi there. Well, I'm proud of you for setting a boundary. We all have to do that from time to time. If you feel she was a user and you were her target, that makes it much easier to end the friendship. Well, if you can call it a friendship.
One sided things like what you've described aren't really a friendship. Hurts much less to end that type of thing.
It's different than if it were a friend that you shared genuine good times with and you've just grown apart or irritated with the person over time. That can happen and in those situations, I see it as less anyone's fault but just the way life goes.
But that isn't what you are talking about. This woman tries to take advantage of you and makes you uncomfortable. I can see that you wish you hadn't answered the emails and I agree. Is there any down side to letting you know that you are done? If not, then a short note saying that you've thought through things and you are feeling as if the friendship isn't working should suffix to end it and have her leave you alone (although I'd expect a bit of back and forth since it sounds like this will be a surprise to her --- that you really don't have to do if you don't care to. You are not obligated to give any further explanation.)
So, maybe one final email and be done with it. You are a personable person that clearly makes friends easily---- you don't need someone that is using you to insert themselves into your life again. You don't need that at all. peace and luck to you