A 20-year-old female with lower quadrant abdominal pain, fever, and a foul-smelling discharge likely suffers from which of the following conditions?

The symptoms described—lower quadrant abdominal pain, fever, and foul-smelling discharge—are indicative of pelvic inflammatory disease (PID). PID typically occurs due to infections that ascend from the cervix or vagina into the upper reproductive tract, often associated with sexually transmitted infections such as gonorrhea and chlamydia. The presence of foul-smelling discharge is particularly suggestive of an infectious process and aligns with the clinical presentation of PID.

In contrast, while other conditions like appendicitis and ovarian torsion can present with lower quadrant pain and fever, they do not typically produce a foul-smelling discharge. Appendicitis often results in localized pain that may migrate towards the right lower quadrant and involves symptoms such as nausea and vomiting without a discharge, whereas ovarian torsion presents with sudden onset severe pain and may lead to nausea but does not typically involve discharge at all. A urinary tract infection, while capable of causing lower abdominal pain and fever, is more commonly associated with urinary symptoms like dysuria and frequency, rather than the gynecological signs and symptoms described in this scenario.

Thus, the combination of the symptoms points firmly towards pelvic inflammatory disease as the most likely diagnosis in this case.