Endometriosis should also be considered in Differentials in young female patients . The cause can be ruptured endometriotic cyst which i suppose can be secondary to enlarged size or a possible blunt trauma.
A young female patient with lower abdominal pain and free fluid---Endometriosis is another possibility which should be kept in differentials--- A ruptured chocolate cyst.
Clinical correlation with menstrual history, radiological investigations and CA-125 levels would be helpful.