What is the ruling on the attendance of an un-hijabed coordinator (uncovering her head and face) at meetings for teaching the Arabic language and Islamic education in the mosque?

The sister should be advised gently and kindly that Allah has mandated the hijab for Muslim women, and that it is unanimously forbidden to uncover one's hair in front of non-mahram men. The sinfulness of this display increases when it occurs in a mosque, which Allah has commanded to be elevated and glorified. Sins committed in sacred times and places are amplified. It is not permissible to associate with this girl if she insists on not wearing the hijab.