Is it permissible for a grandmother to invest her minor granddaughter's money and consume the profits from this investment, or do the profits entirely revert to the granddaughter?

If the girl has not reached puberty, her financial guardianship belongs solely to her father, and he is responsible for safeguarding or investing her money. He may also delegate this responsibility to someone else.

However, if the girl has reached puberty and is mature, her money should be handed over to her for her to manage, and its profit should be divided between her and her grandmother if the grandmother invested it, according to their agreement.

If the grandmother invested her minor granddaughter's money without the permission of her guardian, or without her permission if she is an adult and mature, then the grandmother is liable for any losses incurred. Regarding the profit, there is a difference of opinion among jurists: the Shafi'is and Malikis hold that the profit belongs solely to the grandmother, while the Hanafis and Hanbalis believe it belongs to the owner of the money. Sheikh al-Islam Ibn Taymiyyah chose to divide it between them.