Female equivalent of 兄台
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.