Is it permissible to take a sum of money from the father's wealth, equivalent to the value of a diamond set that was given as a "subha" (a gift given to the bride on the morning after the wedding night) to the wife, then taken from her with her consent at a young age because her family could not afford to provide a set for her brother's wedding, knowing that she had requested it before her mother's death but they refused, and she is now in dire need of money? And does she have the right to claim this right and not relinquish it?

If your father guaranteed the payment for the diamonds that were sold, then there is no objection to taking your right from his money that he entrusts to you, even without informing anyone, as long as it does not lead to a great corruption such as severing kinship ties.

However, if your father did not guarantee the payment, then it is not permissible for you to take anything from his money, because you have no right with him in this case.

It must be noted that it is not permissible to exceed the limits of the right that is firmly established for you as a debt owed by your father.