For me, I won’t explain to her directly. I will explain to my husband to let him know the consequences so that he himself know how serious it is and then he will think of a way to bring it up to his mum. Many times I too have different ways of handling baby and can’t accept certain ways of her handling my baby. Small things I will keep quiet and let it go, if it’s something I think will endanger my baby, I go straight to my husband and makes sure he conveys it sternly. I don’t bother showing my mil any articles because she will just brush it off with “aiya nothing will happen”.
Are you close enough with your MIL?does your MIL trust you as she trusts her son? Based on my experiences, if the answer of my questions are No. It's better you told to your husband to tell his mom about SIDS based on medical expert articles cause although you told to your MIL about that and show the articles, she won't hear you and will keep same things.. Hope it works..