Is it permissible for a working woman, for whom it is difficult to remove her hijab, to wipe her face with water, and is it permissible for her to wipe over her hijab instead of her hair during ablution?

It is not permissible for a woman to wipe her face instead of washing it during ablution, because what is obligatory is to wash the face, not merely wipe it, as Allah Almighty says: "O you who have believed, when you rise to [perform] prayer, wash your faces." Fear of wetting the headscarf or the time taken to remove it is not an excuse that permits abandoning the washing of the face.