What is the ruling regarding the salary of my mother, who works as an accountant at the Post Office and cannot leave her job or transfer to another department? Is her money considered unlawful (haram) or mixed (mukhtalat)? Is there a prevailing legitimate (shar'i) interest that would make her salary lawful (halal) in this situation?

If the mother is compelled to work to earn her livelihood, and finds no permissible work other than it, then she is allowed to remain in it until she finds another job. However, if she is not compelled, then it is not permissible for her to remain in this work, which necessitates direct involvement in haram (forbidden acts) and assisting in it. The salary received for the forbidden work would then be unlawful (haram).