Kso, I have a friend well I THINK is a friend and like some of my friends tell her secrets cuz we thought that?

We can trust her right? Well one of my friend's told her a secret and to NOT tell anyone! But the next day or so EVERYONE knew! Even when NO ONE told her she finds out. One of my friend's was crying cuz of her because one of the secrets of hers was REALLY deep. And when people starts to know that it was her telling people they were mad at her. And NOW she's trying to twist it around! OH. and I think she's trying to be 'popular' by like stealing some of MY friends away. And always makes plans with them right in my face! Like seriously she's never gonna have friends when she's acting like this! But NOW everyone knows that she's a liar. But she keeps doing it. What can I do? Please and Thankyou.