Is it permissible to deliver lectures to women in mosques due to the difficulty of finding other venues for Islamic lessons?

A woman is permitted to stay in the mosque just like a man, unless she is menstruating or in a state of ritual impurity (janabah). This is indicated by the Prophet's (peace and blessings be upon him) prohibition of a menstruating woman staying in the mosque. Therefore, there is no harm in holding lessons for women in the mosque, although it is better for them to be held outside the mosque to enable menstruating women to attend and to spread the benefit more widely.