What is the Sharʿī ruling regarding a married woman gifting a sum of money to a child she adopted to secure his future, noting that the gift has not yet been taken possession of and that the woman has heirs, and can this gift be proven through a will or by other means?

If a woman donates an amount of money to a child during her lifetime, and she is of sound mind and mature, and the money is taken possession of, then the money becomes the property of the child. However, if possession is not taken until she dies, the child does not own the donation except with the permission of the heirs. And if she bequeaths this money to the child to take possession of it after her death, then the child is only entitled to a third of the money, and the rest goes to the heirs, unless they permit otherwise.