Am I wrong? 😡

So apparently my sister has an issue with my husband and neither of us knew about it. Someone I know found on her Twitter that she was talking crap about him behind our backs. Am I wrong to be pissed off about that? If she has a issue with him instead of talking crap about him on social media behind our backs she should talk to him. He’s even said he’s be happy to talk to her about it and work it out but she never replied.

Am I wrong to be upset/mad? 😡