Am I wrong for not defending my friend?

I have a best friend named Lesley. We have been friends since we were 4 and 5 and now she's 19 and I'm 20. Nearly 15 years. I ended up making friends with some girls in Chemistry class at college this semester and Lesley started hanging out with all of us. My friends don't like Lesley because they think she's annoying. Lesley can be a bit annoying but she means well. She lived with an abusive aunt and wasn't really allowed to talk at home so when she would get with friends she would super excited. She's hyperactive and a very happy person. I was at my friends house and Lesley was coming and they said they wanted to tell Lesley off. I explained what I did you guys about her just being a happy person but they said she was still annoying when they got their, my friend Claire said she had something to say and Claire told Lesley she was the most annoying person she ever met. And everyone just starts laying into her about her they don't like her and how she's annoying and they actually want to punch her most of the time and just saying really hurtful things. She was on the verge of tears and asked if they wanted her to leave a they said yes and she walked out fast.... And I said nothing that whole time... After she left they were talking about her and I feel so awful. But what was I supposed to do... Ugh am I a horrible friend?