Disrespectful in-laws????

I am highly HIGHLY upset. My husband I do not post our child on social media. I don’t get a long with his family especially his sister. Everyone in our life including his family knows that we don’t post our child. I have had stalkers in the past on social media and still do (last stalker incident was this week). So naturally I am afraid for my child’s safety. I just found out that his sister has been posting my daughter on her Snapchat FOR MONTHS. We live in the same house and she has been posting her every chance she gets. Idk who and who she has on Snapchat that I don’t know. I am so beyond angry. Not posting our baby is a choice me and my husband made TOGETHER. We don’t post her at all and when we do we put a sticker over her face but for the past few months we have not posted her at all and we don’t plan to. She knows we don’t want anyone posting her. I am FUMING. Am I overreacting? I made my husband aware but idk what to do. I feel so disrespected.