Got a message from an old friend

Well, and don't know, if it is a good or a bad thing, but it made me uneasy, so I decided to post it. I needed acouple of minutes to really write it down, beause I don't know, if it's a good idea to post it, but I think you can understand what I mean, so I'll wirte it down for all of you to ask, what you would do.

I don't know how to start. Normally I would have to write down a long story, but this time, I'll make it short. I'm in grade 11 now. I have problems with people since I was in grade 7. I went into a new class in this year and there was just one person, i really talked to (there were 2 other girls, too, but it's too long to write it down now). There was this girl, and I liked her. Our friendship was always... I don't know how to describe it, it wasn't a normal friendship, or for me it wasn't. I don't now why, that makes it weird. One year later I realiced, what a person she was. She was beastly to others, espacially to kids and that's one point, I would never understand. I couln'd understand, why she always beated children, who were younger than her and things like that. Time went by and we were together at school all the time, although I didn't like her anymore. In grade 9, she began to say terrible things to me. We didn't really talk anymore, we just sat there, waiting for the day to pass. it was awful. One day, she started to send me messages on my mobile phone, she wrote, what a terrible person I am because i ignored her. (i didn't, I was just scared of her and of finishing what was called friendship.) Well, more time passed, an ich got scared of my mobile phone (I needed a long time to top it, now it isn't that wore anymore). Sorry if I can't discribe it better, I know you do understand, what was terrible and why I got scared, it isn't easy to talk/write about it. So it went on like this, it got more terrible and I was scared of going to school, but I just wasn't able to make it stop. I don't know why, but i wasn't able to. The good thing was, that this school ended after grade 10 and I just waited for the time to pass and since the last school day, I didn't talk to her anymore. I have to think about her often, and I'm scared to see her sometimes somewhere in the supermarket or something.
Last thursday was my birthday and now she wrote me, and I just don't know how to awnser. One one hand I want to tell her, that I hate her and that she never should talk to me again, but on the other hand, I want to ask her, how she is. Or maybe, I shouldn't awnser.
I don't know. Have you ever been in a similar situations or do you just can help me. A 'I understand how you are feeling' would be enough, too. I'm going to post this now, instead I would delete it again.

What kind of message did she send you this time?
If you don't have any desire to talk to her, you don't have to. It's not your responsibility to take care of her, or fix her. You sound like a good person that you would want to, but it's not fair that this has to fall on your shoulders.
Recently, I had to stop talking to someone who made me feel unhappy, and I feel guilty about it. But they're strong too, and they'll be able to go on and hopefully grow. I think it's probably the same with your old friend.
It's your decision what you want to do, but you shouldn't feel guilty if you don't choose to talk to her anymore. Sometimes the best thing you can do for someone (and yourself) is to break the pattern of bullying or abuse.
Good luck