Is it normal for sis to overreact to something someone said about me?

Okay, so I pissed someone off and he posted a long rant about me on Facebook. It was no big deal to me, anyone who liked me would just think he was being an asshole. I was sitting next to my sister when she was reading it on her phone though, she covered her mouth then started crying. I hugged her and asked her what's wrong and she said people were saying bad things about me. She said I'm perfect and nobody should be mean to me. She was really upset honestly I hadn't seen her that bad in awhile. I told her it's okay and just to not look at it. I had to take her phone and hug her until she calmed down which was a few minutes. It's no big deal and I think she shouldn't cry over it.