All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.
As long as the work of your mother is permissible in principle, then her salary is halaal. Hence, it is permissible for you to benefit from her money that is earned from this job, but you have to advise your mother, invite her to Islam, and let her know about the good traits of Islam.
If you do so, then this is indeed one of the greatest acts of kindness and dutifulness to her. Perhaps you will be a reason for her guidance to Islam, saving her from Hellfire, and her becoming successful in this life and the Hereafter.
Allah knows best.