My sister in law is pregnant and I want to help

My brother and his SO are expecting a baby on Oct 1st. They're not very prepared and I want to help her out and give her some advice for her pregnancy. I'm studying pregnancy and child care in university right now and feel as though I could help her tremendously however she has made it clear she doesn't want any help. Which would normally be okay but she isn't taking prenatal vitamins and she's still smoking cigarettes so I want to know how I can help her make some decisions without coming off as a bossy know-it-all?