What is the ruling of Islamic law regarding a girl's desire for gender transition from female to male, her rejection of her female nature, her relationship with another girl, her desire to marry her, and her undergoing hormonal treatment for this purpose, given her brothers' rejection of this?

It is not permissible to proceed with a gender reassignment surgery unless medical examinations prove that the reproductive system of the person concerned is male, while outwardly appearing female. In such a case, there is no objection to performing it. However, if the examinations show that female characteristics are predominant and that her reproductive system is female, then she is not permitted to undergo this surgery.