Is it permissible to benefit from money deposited in a usurious bank, which my mother deposited to help my sister and me get married, given my knowledge of the suspicion of usury and my mother's refusal to dispose of it?

You must continue to advise your mother about the gravity of usury (riba) and that it incurs the curse of Allah, urging her to deposit her money in an Islamic bank or entrust it to a trustworthy and reliable agent for investment. If she responds, then praise be to Allah. If she does not respond, then you have fulfilled your duty. As for taking from these usurious profits, it is not permissible for you to benefit from them if you are wealthy. However, if you are poor and in need, there is no harm in you benefiting from them.