Is it permissible for my mother to dispose of my grandmother's money and donate from it with the intention of charity on her behalf and on behalf of her deceased parents, especially since my grandmother has partially begun to lose her memory and does not ask about her money?

It is not permissible to dispose of the grandmother's money except with her permission, if she is of sound mind. If she has lost her mental faculties, then her money must be preserved, and it is permissible to spend from it on her basic needs such as food, clothing, and medical treatment, and to pay its zakat. As for donating, giving charity, or gifting from her money without her permission, it is not permissible. In the case of loss of capacity, a guardianship must be obtained from the court to dispose of her money, and the guardian is not permitted to donate from her money; rather, he should only dispose of what is necessary. Any ring taken without her permission must be returned.