Why do some girls do this?

Sorry if it’s long, I just need to rant

I was friends with this girl (let’s call her Becca) for close to ten years. She made a friend (we’ll call him Sam) who had a crush on her but she didn’t like him back. Through her, I also became friends with this guy and it was cool. Then she cut him off because she claimed he was obsessed with her and would always post about her but to be honest, he never truly did. Did he have a crush on her? Yes but we’re all adults so it’s not like he was head over heels with someone who didn’t give back that energy. Becca and I ended up distancing ourselves over time. She was in a really toxic relationship but I was always there for her, she just stopped answering me. Sam and I hung out for the first time in a while and after she saw that she texted him claiming that him and I were both ugly, in a relationship, and that he’s crazy obsessed with her and then she blocked me. I have a boyfriend which I’m sure she knows since I post him all the time but it came out of left field. When I tried to talk to her about it, she never answered. Why talk shit about me if you’re not going to deal with confrontation?