I'm a guy, I've never had a girlfriend pregnant so my advice isn't as useful as other peoples here. Just a fore-warning.
I would say abstain from smoking anything.
If shes going to do it anyways. Practice harm reduction. Don't use shwag/mids grown and cured with nasty fertilizers remaining in the final product. So if shes a patient at a medi-club she'd be safer off in my opinion.
Also don't smoke anything. It's just not healthy for her, and her body is going to be on over-drive during the pregnancy. Maybe cook with it, or vaporize only.
Don't have her abusing it how she would if she wasn't pregnant. Lower the frequency of use if your not going to stop it.
That's if she's going to do it anyways.
Anyways, this is a big-time for you to step up and take care of her. So if she chooses to abstain from smoking, I'm sure it would be really supportive if you at least slowed down and didn't use it infornt of her. Remember you need to support her though this, and pregnancy is no cake-walk!
Congratulations on your soon to be born twin widdle babies!