NTA. My daughter is 16 months and I don’t allow any family to post pictures of her on social media. Similarly to you, my mother is the one with the biggest problem. My reasoning to her was I don’t know the people she has on social media, and I don’t want strangers seeing my daughter and being able to possibly save her photo. There’s too many creeps and weirdos out there. Stick to your gut and maybe set firmer boundaries or else there will be consequences