Right, for the love of all that is holy, put proper words in your posts! if you want people to give you advice, it generally helps if we can understand what on earth you're trying to say! Seriously, I know it's not that hard. Look, I've just managed a whole heap of sentances without really trying!
Write a job application using that kind of writing - see how far you get.
Anyway. To the point.
Is she really a mate of yours if she's stealing from you? you need to talk to her directly, straight to the point - "Look, not being funny, but I've noticed that every time you come round my house, things of mine go missing, is it just a coincidence?" See what she says. Generally people can't look you in the eyes if they're lying to you.
Also, maybe the 'hanging out with the popular kids' thing was just an attempt to make herself look cooler. Maybe she has self esteem issues that you could help her with?
Lastly, perhaps she was jealous of your GCSE results and that's why she didn't even say well done?
Overal, seriously just have a word with her. If you're still not happy after that, then just say to her "I'm sorry, I can't be friends with someone that I don't trust" and move on with your life. You can ignore her texts, just delete them as you get them.
Good luck.