Is it obligatory to divide the mother's gold and jewelry equally among all heirs, especially given that the mother bequeathed this gold to one of her daughters?

The mother's wish that her inheritance be solely for her daughter has no effect. If there was a will to that effect, it is a bequest to an heir, which is not enforceable unless the rest of the heirs agree. This is based on the Prophet's (peace be upon him) saying: "Indeed, Allah has given every rightful person his due right, and there is no bequest for an heir." Therefore, the inheritance must be divided among the children according to Sharia, unless they willingly relinquish their share. It is not permissible to monopolize the inheritance without the consent of the other heirs.