Trusting the wrong people

Once again i trusted the wrong people. I have a friend in my graduating class and i have her on facebook, theres these different applications that you can add and i added that one that asks different questions about my friends and i  either say yes or no,  i found out that someone didnt think i could keep a secret and i'm confused because when it comes to my friends, i keep things to myself, if they trust me enough to know a part of their life, in respect for them i keep everything to myself. I confronted this person and she said she didnt remember doing it. I dont recall doing anything to her, i didnt hang out with her in high school so i dont really know her so i dont understand why she would think that if she hasnt told me anything. I have proof that she said it, it said the time she did. It hurts me to know that she thinks that. I would never betray any of my friends trust.  I honestly dont know what to do now.