Is it permissible for a woman who wears the niqab to temporarily remove it to obtain a teaching job, with the intention of wearing it again after being appointed, in order to meet financial needs and help her family, fearing rejection because of it?

A woman must cover her face and hands. It is not permissible for her to uncover her face before non-mahram men unless there is a legitimate excuse. If she is in need of work and cannot find any other, then there is no blame upon her for uncovering her face to the extent of the necessity. Once the necessity ceases, she must cover it.