Is it permissible to benefit from the mother's money if she works in a usurious bank?

Your mother is not permitted to work in a usurious bank, because that falls under aiding in sin and transgression, and the money she receives for this work is unlawful (haram (definition)) money. She must repent and leave this job immediately.

If your mother has money from a lawful source, then there is no harm in accepting her gift. However, if she has no money except from her unlawful work, then it is not permissible to take from it, and she must dispose of it by giving it to the poor and needy. This is unless she herself is poor and in need, in which case it is permissible for her to take from it what suffices her and her dependents.