Why is it so hard to tell a 16 yr old something

Pretty much all my grandmas life she has bought fake nails that you glue on. Basically she superglues plastic to her nail beds. That’s really bad for your nails. Water and sweat gets up under there into the nail beds and causes fungus. My grandma has had fungus on her nail beds for years and it’s to the point she doesn’t have fingernails anymore. She gave my sister a whole bunch of fake nails and SUPER GLUE and I’m trying to tell her that she’s gonna have Fungus on her fingernails like our grandma but nooo that won’t happen “because I keep my nails clean”🤦🏻‍♀️🤦🏻‍♀️ she saw grandmas green fingers and still claims it won’t happen. She has like a freaking lifetime supply of fake nails and glue now so she’s gonna have to learn for herself when one of those fake nails come off and her fingernail is green