MIL kissing baby

So even before my son was born my MIL would say “Oh I can’t wait to kiss those lips” and other similar things. I addressed it with her and said no one would be kissing him on his lips for many reasons. After he was born she continued saying how she can’t wait to kiss him on the mouth and each time I would remind her we are not allowing ANYONE to kiss him on the mouth. I had this conversation with her maybe 10 times. Well tonight she was over for dinner and when I was putting him to bed she went to say goodnight and kissed him ON THE MOUTH. I flipped the fuck out! How disrespectful of her to do that! She knew our rule and blatantly ignored it. Makes me wonder the few times we have had her watch him if she has kissed him on the mouth. I’m so furious! My husband agrees with me but didn’t say anything to his mom tonight. I told him he needs to talk with her tomorrow about it so she fully understands why I yelled at her. Wtf is wrong with her?!?