How to help, plz..

My sister is 33wks with her first. Shes a drug addict and idk how to help her. She stopped P when she found out she was pregnant but still continued weed and smoking. The father is an addict and has many baby mamas. I just dont know how to help as she shuts all her family out that truely care in favor for her fellow addict group of friends whos only goal is to get high and dont really care about her at all. She honestly doesnt think shes an addict or has mental health issues that need help with. Its so hard to watch. My family just try's to help best we can but alot falls on deaf ears.