friend flirts with boyfriend

hello. A while ago I found out some information about my bestfriend that concerned me. She had been flirting with my boyfriend in secret. I had been distancing myself from her for a while and she recently found out I knew about it. Shes trying to defend herself by saying she wasnt the one saying those things and instead my boyfriend was. Theres screenshots of her "joking around" saying he was cute and asking him for hugs and stuff. There was also a screenshot of my boyfriend talking to his friend about what she did on call. Basically on the call she was showing her thighs and being really weird and saying inappropriate stuff towards him. I basically said i knew what she did and that it was in the past and im trying to move forward with my life. What should I do if she continuously denies what she said or even spreads rumors about me?