At this point as I comment, you have 15 fellow members here all prescribing, more or else, “watch that witch”, Initially, I was wondering if the in-law spoke English as a second language and that in her native language “pinch” the baby meant something like “kiss” or just some harmless gesture that was more figurative than literal. The fact that she argued with you after you rightfully protested rang alarm bells. It suddenly reminded me of what my own dad did to my infant daughter when she was still unable to sit up straight. If it was a language barrier issue, couldn’t your partner clarified what was then lost in translation? But since you haven’t mentioned any cultural or linguistic aspect, I hope you’d be holding your child protectively close to you and ideally having your partner watching so he doesn’t later say “oh, you’re just exaggerating.” Praying for you and your baby!