What is the most likely diagnosis for a 17-year-old female who has never had her menses?

The most appropriate diagnosis for a 17-year-old female who has never had her menses is primary amenorrhea. Primary amenorrhea is defined as the absence of menstruation by the age of 15 when secondary sexual characteristics have developed or by the age of 13 when they have not. In this case, since the patient is 17 years old and has not yet menstruated, primary amenorrhea is the most likely diagnosis.

It is essential to consider that other conditions, like polycystic ovary syndrome (PCOS) and hypothalamic amenorrhea, typically present with menopause later in adolescence or in adulthood after having had normal menstrual cycles, making them less likely in a person who has never menstruated. A granulosa cell tumor could also cause amenorrhea but usually manifests with other symptoms like abdominal masses or hormonal imbalance in women who have previously menstruated. Thus, the absence of menstrual history in this scenario strongly supports primary amenorrhea as the correct diagnosis.