Hi Thanks for posting your query on HCM. I appreciate your concern for your fiancee. I have gone through the problem described in your query I am of the opinion that she seems to be suffering from a sweating disorder known as Hyperhidrosis which is focal or localized to her butt crack. Hyperhidrosis is a condition in which a person has overactive sweat gland resulting in excessive and unpredictable sweating. It is most commonly seen during warm temperatures, when they exercise, or in response to situations that make them nervous, angry, embarrassed, or afraid. It can occur without such triggers. It may be controlled with strong anti-perspirants like 10% to 20% aluminum chloride hexahydrate which is applied on to the affected areas. If there is no improvement, you may consult a dermatologist for the other treatment options like Iontophoresis & Injection Botox. Hope these suggestions could be helpful in getting her treated. A feedback is appreciated.