Final answer:
The strongest risk factor for primary amenorrhea in the question scenario is a family history of polycystic ovary syndrome (PCOS), as it has a genetic component and can cause hormonal imbalances that prevent menstruation.
Step-by-step explanation:
The question asks which finding is a risk factor for primary amenorrhea in a female adolescent client. Among the options provided, both a family history of polycystic ovary syndrome (PCOS) and a history of eating disorders are recognized risk factors for primary amenorrhea. PCOS is an endocrine disorder characterized by high levels of androgens which can interfere with the menstrual cycle, and eating disorders can lead to hormonal imbalances that affect menstruation as well. However, since the question specifically mentions primary amenorrhea, which is the absence of menstruation by age 15, a family history of PCOS would be a stronger risk factor given its genetic links. Excessive exercise is also a risk factor, as it can cause amenorrhea through energy deficiency affecting hormone balance, while a history of early menarche is not typically a risk factor for amenorrhea.