Female equivalent of 兄台 In ancient China,  among males there was the polite appellation 兄台。 Was there an equivalent term for women, or did it not develop due to 男女授受不親？
Among the time when boys call each other 兄台, which should be around 唐宋年间, you can call girls 娘子/姑娘 in the same conversation context. 

Another term similar is to call girls 小姐, which refers to young girls who usually have been properly educated and have a decent family. However, the corresponding word for 小姐 for males is 公子.