Smokng and pregnant, can anyone help?

I know this is a no brainer but I am 4months pregant and i stopped smoking cigarettes a month back. It was hard for me but i did but my friend (bf) is about 6 months and she still smokes. Not as much as she did before but she still does. Im worried that somthing can happen to the baby but i cant stand an argument with her because both of our mothers smoked with us and we are fine. Does anyone know what i can tell her to atleast make her tink abiut it? thanx