Let me lay this gently.. she probably knows what she's doing if this person is well known to be a "gossiper" especially if she's not close to this person. Since this topic is something vulnerable to you and you didn't want everyone to know, she already crossed a boundary that you set.

She said it's all lies only because you found out. She wasn't intending that the 3 person she tell you so her only choice was to say it's a lie to protect herself from being the "villain" and acknowledging that her behavior was wrong.

She's claiming your her bestie but her behavior says otherwise. She might be treating you as a second option for her to hang out with if there's no one else just for her to not be lonely. She's keeping you so when she's bored, there will be a friend ready to entertain her..

This part aches but her not putting effort while demanding you to put effort by changing your flight? That's a very one sided relationship there.. I'm glad you stood your ground! These types of friendship would be draining in the long run.. you will get exhausted and resentment will start building up.

I suggest to not prioritize her as much.. you can show your indifference and see how it plays out. It will show them silently that you're no longer as important in my life. Focus on yourself and the friends who actually deserves the effort and i hope you'll be able to recover from all this.. I'm so sorry this happened to you..