My oldest friend since primary school has really changed. She acts really flirty and sometimes bitchy and some of my friends and myself had a big fight with her last year... She promised to changed but she hasn't.

We all change through years. i think you not the same, that you've been in primary school. My best friend became kinda bithchy too but I love her the way she is, although sometimes I feel embarressed for her and sometimes she irritates me
Now you have choice: you can leave her and find new friends or try to love her as she is. But you can't change ppl. She only can pretend to save your friendship (though I dont think that's a good way)

lots of people change. i'd sit down at chat to her. maybe start off ther conversation by bringing some sweets and offering her one, as a starting point. then bring the subject up with her about what you've just told us. if she's a true friend she'll understand.

i'm having friend trouble at the mo too. this is what happened to me:

my bestfriend recently turned on me because when we were talking, i told her of this boy i liked, and i really did like him, he was amazing and i was totally made for him. my BFF said she'd help me go out with this boy, and she said she'd speak to him. i asked her if she was sure cos i was pretty confident i could do it myself, but i trusted her to help me out. instead, she turned him towards herself and i later found out she liked him also, but this was after i'd already said i liked him. she did not help me at all!! while she was talking to him she had told him all these terrible lies and fake-cried and everthing. now she is with him. i feel like such a fool for letting her "help" me. worst of all, i see her every day at school, and i have to accept that the guy of my dreams is now taken; by my so called best friend, who pulls his tie and pokes him in the stomach.
also, everytime she sees me she rips my work, really discreetly so no one sees, or tips water on my work, or pushes me against the wall or throws my lunch in the bin.but she never gets caught cos she's such a goody two shoes to the adults.
so i'm pretty sad at the mo. mostly cos of losing my guy. :,(

The real question is do you still wanna be her bestie..... Because one of my frinds didi that to me and i forgave her tha 1st and 2nd time but the 3rd time i said enough is enough and i told her if she was going to keep treating me this way we couldnt be friends anymore she said fine for a littel while i couldnt even look at her but now we are friends NOT best firends not even close Friends just friends. so see if you get anything from that!!

Try to have a serious talk with her. If things don't change, then she obviously doesn't care about whether or not she's hurting you; I'm sorry.

well if you gave her a second chance she should have stopped I wouldn't b her friend anymore

I guess she's acting that way because people can change and maybe as she got older she started to care more about other things explaining how she acts now (flirty & bitchy).
I think also that she keeps making promises that being broken to you to pretend to reasure you or just to stop u from bothering her (no offence).
I got in the same situation before so I know how u feel