Is it permissible to give charity and establish an endowment on behalf of a grandmother who is not compos mentis due to dementia, and is it permissible to give her daughters from her monthly salary, knowing that one of them has a low income?

Such a grandmother must have a guardian appointed over her money to preserve it. If she has no guardian, her case must be brought before the Sharia court to appoint a trustee over her assets, protecting them from her own mismanagement or that of others. This guardian is not permitted to dispose of her money except in ways that benefit it. Therefore, it is not permissible for him to give charity or donate from it, as the restricted person has no share in such actions. Consequently, it is not permissible to give charity on her behalf, even to her daughters, nor to establish endowments for her from this salary.