I was 13 (now 14F) when I went to a sleepover at my friend R's house (now 14F). R is very nice but an anxious pushover. During the visit, R’s younger sister D (then 8, now 9F) got mad and tried to hit R. I stepped in front of R and grabbed D's arm, D yelled at me to let her go, but I made her promise not to hit R before letting go. D complained to their parents, but when I explained what happened, the parents agreed I did the right thing and talked to D about it. Later on, after R had left our mutual friend group over unrelated drama, while in a conversation R's little sister came up, I told this story and a friend said that R had talked to them and she said I had actually slapped D for "being annoying", friend was confused since thats not like me. I cried after I grabbed D's arm to stop her from hitting R and, R even comforted me at the time. While my friend group entirely believes my side of the story, I am still furious that I defended R only for her to turn around and lie about me.