Is it permissible for a mother to keep a platinum certificate if she is unable to trade with it, but uses its proceeds to help with household expenses? And if it is not permissible, is it then permissible to wait until its term ends to dispose of it without losing the principal?

Investment certificates with a fixed return are usurious loans forbidden in Islam. If breaking the deposit would lead to the loss of part of the capital, and this loss cannot be borne due to need, then there is no harm in leaving the money until the term ends, then withdrawing it and disposing of its interest by giving it to the poor and needy. It is not permissible for the one who receives this interest to benefit from it, unless they are poor and in need, in which case they may take from it according to their need.