E. Obturator hernia: This is the most likely diagnosis because obturator hernias are more common in elderly females and can cause small bowel obstruction without an obvious external hernia. They are often difficult to diagnose and can be missed on initial examination.

C. Gallstone ileus: This is a possible cause of small bowel obstruction in elderly females, especially if they have a history of gallstones. Gallstone ileus occurs when a gallstone passes through a fistula into the small intestine and becomes lodged, causing an obstruction.
B. Volvulus: A volvulus is a twisting of the small intestine that can cause an obstruction. It is more common in elderly patients and can be caused by a variety of factors, including adhesions or abnormal intestinal rotation.

A. Small bowel neoplasm: Although less common, a small bowel neoplasm can cause an obstruction and is important to consider because it can be a sign of a more serious underlying condition, such as cancer.
D. Abdominal abscess: An abdominal abscess can cause a small bowel obstruction by compressing or adhering to the bowel. It is crucial to consider this diagnosis because an abscess can lead to severe consequences, including sepsis, if not promptly treated.

Intussusception: This is a rare cause of small bowel obstruction in adults, where one segment of the intestine telescopes into another, causing an obstruction.
Inflammatory bowel disease: Conditions like Crohn's disease can cause small bowel obstruction, although they are less common in the elderly population without a prior diagnosis.
Adhesions from previous surgery: While not rare in the general population, adhesions causing small bowel obstruction might be less likely in an elderly female without a history of abdominal surgery, but still, it's a consideration.