Did the niece squander the trust and incur sin by obeying her testator—who was unauthorized to issue such decrees—in building a mosque with all her money, which led to a lack of funds for her treatment? And what is required of the rest of the family regarding this lady?

The purpose of placing a woman under interdiction (hajr) is to safeguard her wealth from mismanagement. Therefore, any disposition of property by an interdicted person is not effective unless approved by her guardian (wali). It is not permissible for the guardian to dispose of her wealth except in ways that benefit it; thus, he may not give charity or make a gift from it. If he does so, he is liable for what he has donated. The action of the female guardian (wasiyya) in donating from the aunt's money has no effect and does not relieve her of liability. She is liable for what she donated. The expense of the woman's medical treatment is the responsibility of her female guardian, to be paid from the woman's own money, and it is added to what the guardian donated.