A 58-year-old woman presents to the emergency department with acute onset severe pain in the right groin and lower abdomen for 6 hours. She reports a small, firm, irreducible lump below the inguinal ligament, medial to the femoral vessels. On examination, she is distressed, with tenderness and guarding over the lump. Bowel sounds are present but reduced. Abdominal X-ray shows small bowel loops with air-fluid levels. What is the most likely diagnosis?