There is not "traditional" clothing for a Jewish woman. They will wear a longer skirts (past their knees) and shirts with sleeves that go at least to the elbows if not to the wrist. Married women will cover their hair with different types of scarves or wigs (my mother wears a tiechel usually).
Many prefer light shirts and dark skirts (my mother usuallly wears black or dark skirts) and plain light colored fabric that does not draw attention.
Your friend does not have to wear maternity clothes. I don't and I am 36 weeks pregnant. I personally think they are very expensive and don't have a lot of styles for what I like.
Usually I just buy extra big clothes and wear the pants below my belly, so it's still comfortable. I also wear my husbands clothes too.
Have her find stuff that she is comfortable in, and do that, why wear maternity clothes when you only wear them for a short time. Especially since your body is constently changing while you are pregnant you could end up buying way too many clothes because they will end up not fitting later on.