However, i stand by my statement that if a parent is impaired by alcohol or drugs and unable to care for their child, someone needs to be there for the child, at the times when Mum is unable to provide care.
But, as a former pot-smoker and having lots of friends who *do* continue their habit after becoming parents, I can say that in my personal experience (as in, seeing others, I stopped using before TTC) that marijuana use doesn't necessarily 'impair' a person, or impact negatively on their ability to care for their children. The effect you get from a few bongs is vastly different to what you get after a few drinks, and of course an entirely different story to 'hard' drugs like heroin, speed etc (where yes, a person truly does become impaired).
I suppose what I'm saying is that a parent can smoke a fair bit of pot and not have it affect their parenting ability - if they can function normally in day-to-day life in every other area while they're buzzed, the kids are very unlikely to be at risk of any harm.


Anyway, onto the actual question, which is worse... I personally would say the booze. Obviously it all depends on the frequency and level of consumption, but as the OP said, this particular person may not drink every day, but does drink a relatively large amount on the frequent occasions she *does* drink. Alcohol does some pretty scary things to adults, just think of what that does to a growing foetus. Marijuana though... yes, there are dangers, but they're more akin to those associated with smoking tobacco - lower birth weight, risk of prematurity (which are both also associated with alcohol abuse, and therefore it's neither here nor there as far as I'm concerned), and heightened risk of SIDS (although how much that has to do with a parent smoking *while pregnant*, or smoking around the baby *after it's born*, I don't know).
Personally, I'd be inclined to say that alcohol consumption is worse than smoking the ganga... Obviously they both have their bad points (and, really, no good points), but I'd be inclined to say that a lot of the 'marijuana = worse' feelings come from people just because it's illegal, whereas alcohol isn't, and it's some sacred right in Aussie culture to get blind-drunk at every opportunity. Illegal, schmillegal. If the gov't could tax it the way they do booze and ciggies, they'd have it legalized in a second. If the gov't could live without the revenue from alcohol and tobacco taxes, they'd outlaw them and make them look worse than ice and heroin.
(Whoa, I'm way off-topic here, aren't I?)

If your friend doesn't seem to show much interest in quitting or cutting out one or the other, maybe suggest she cut down on the booze and try bush (although if one is used to hydro - which is actually quite pure, just a lot stronger as the mind-altering chemicals in it are concentrated when it's grown in water, not leached into the surrounding soil as with bush - it will give you a nasty headache and take a bit more to get you buzzing)??
I don't know. I personally would not use either during pregnancy period, but each to their own. Yes, the baby has rights too, but ultimately it is going to be the mother who has to live with the guilt of knowing she has contributed to any harm suffered by the child (yes, it's unfair that the child suffers too, but where do we go from there - start locking up pg women in padded cells and feed them special diets and ensure they don't do anything at all that might potentially harm their growing babies?).

I hope no harm comes to your friend's baby, fact is though if she has had other children and smoked/drank throughout those pregnancies and the kids have not suffered any obvious ill effects, chances are she'll take the stance of, 'Nothin' wrong with these ones' and not have any 'reason' to change her habits, kwim?

But I do hope all goes well.