As for canabis, which we know is definitely dangerous to a developing baby
Can you find me a link for this? I remember trying to check this when I was pregnant with my first and finding very little. (He's 7 now and fine!)
saying its not anything worse than what she's done in the past 6 months
I can sort of understand this. She's only just found out she's pregnant, possibly doesn't feel 100% great about it and is maybe quietly worried that damage has already been done. I can see how that would result in a certain fatalism and a "fuck it" attitude.
Its certainly too late for folic acid and avoiding blue cheese isn't it?
If its any consolation: I think you need to be very heavily to give a child feotal alcohol syndrome. Think a bottle of spirits a day territory. Social drinking at the weekends wont do it.
Cocaine is not great but the effect is overstated:
Scientists have come to understand that the findings of the early studies were vastly overstated and that most people who were exposed to cocaine in utero do not have disabilities
From Wikipeadia
Smoking is not great but probably not too much milage in giving up at this late stage.
I would not personally be reporting this person to social services unless she is addicted or her life is chaotic and unmanageable for other reasons.
I'm guesing this is someone you see socially at pubs and clubs (hence you knowledge of her drug consumption). If you don't know what her life is like outside of that context, I'd probably leave it.