Good question Srilakshmi !
You have not mentioned how many green teas she drinks daily.
To answer briefly , it is not advisable to drink more than two or three green teas per day, if they are pregnant.
Here are the details:
During the first few months of pregnancy , the fetus needs vitamins to form organs like brain and heart.
Green tea contains ‘ anti oxidants’ which , if taken in more quantities, will decrease the absorption of folate vitamin. Also, they decrease the absorption of iron, which is also needed for both mother and baby.
So , if more and more green teas are drunk during pregnancy , there is a risk of babies being born with defects ( as a result of folate deficiency ).
Hope this helps to advise your friend !
Best wishes.