What should i do about this friend?

For the past 4 years i've been best friends with a girl- let's call her C. We had so much in common and we were really dependent on each other and I saw her like a sister. However, now we have left school, she doesn't seem at all interested in staying in contact with me. I've tried messaging her asking if she wants to meet up but she either doesn't reply or just replies with something pathetic like "Meh I can't sorry" like wtf??? I don't want to keep messaging her because she obviously doesn't want to talk to me. I haven't seen her for three weeks and she was fine with me then but now she's become so distant.

I don't know whether I am being paranoid but since I haven't heard from her for a few days I feel like something terrible has happened to her, or that she may be purposefully ignoring me because she knows I will worry. I just feel so annoyed at her right now. She's basically just pushed me out of her life as if I don't even exist. She's a very important friend to me (at least she was) but I clearly don't mean anything to her. God, I feel so foolish. I bet when college starts in September she'll be messaging me again because i'm like her only friend. Or then again, she could do one of her classic "I'm not gonna turn up and i'm not gonna reply to any messages for a week so you all think i'm dead :) :) :)". She did this an awful lot throughout school. I'm sick of her making me worry about her all of the time!

I'm tempted to just ignore her if she ever messages me back and then continue to ignore her when college starts and just make some new friends so she can get a taste of her own medicine. What do you guys think of this/think I should do and have you ever experienced this with anyone before? This may seem petty and childish but believe me, there's a lot more I could write. It just annoys the hell out of me that she's no longer interested in talking to me now that school has finished. Thank God I have other friends besides her... and even they aren't that reliable