I'm a doctor. I'm a muslim. Clearly you have consulted with a doctor already. You should go back to this doctor to discuss the next steps forward (likely you have already done this). For all practical purposes your sister is a female who is unable to bear children. She would likely require a vaginal exam to know the extent of her abilities to engage in intercourse, and would also require removal of undescended testes. If she is able to engage in intercourse (which she likely can), then all that is required is that she inform her future husband that she doesn't have a uterus therefore will be unable to have children, that simple. I wouldn't get into the details with anyone because it is irrelevant. Your sister is a WOMAN and always will be a woman. Do not involve scholars in the debate because they likely have no idea what androgen insensitivity syndrome is and will make up something so not to sound uninformed. Lastly, your sister is not part of the "third sex" someone mentioned. She does not have any parts that are male. She is 100% female.