Is it permissible to deal with a bank that the mother describes as operating according to Islamic Sharia, while the daughter herself has doubts and misgivings that dealing with it might be forbidden and bring about a curse?

It is not permissible to deposit money in savings accounts or to invest in interest-based (usurious) banks, because it is a forbidden interest-based loan, as stated in the resolution of the Islamic Fiqh Academy. The account must be closed, and the money withdrawn or transferred to a current account. The forbidden interest must be disposed of by giving it to the poor and needy, and one must repent to Allah. If the mother is not convinced, you can withdraw the money, close the account, and then hand it over to her.