The Bais Yaakov movement was created to keep our girls frum. Before Beis Yaakov girls learnt everything they needed to know at home. It was that way for thousands of years. Bais Yaakov was a response to a shas hadchak.
Will a six day school week make our girls frummer than a five day school week? No. So no need for six days. Will a six day school week allow boys to learn more Torah than a five days? Yes. So six days in Yeshiva. And more hours per day. And more days per year than girls. As it should be. This isn’t a contest where we need to compare boys and girls. And surely we needn’t c’v make them “equals”.