Diverticulitis: This condition is common in the elderly population and can cause abdominal pain and rectal bleeding. The risk of diverticulitis increases with age, and the presentation of abdominal pain, usually in the lower left quadrant, along with rectal bleeding, makes it a likely diagnosis.

Colorectal Cancer: Although not as common as diverticulitis, colorectal cancer is a significant concern in elderly females, especially if there's a history of unexplained weight loss, changes in bowel habits, or a family history of the disease. Rectal bleeding and abdominal pain can be symptoms.
Angiodysplasia: This condition involves vascular malformations in the gastrointestinal tract and can cause rectal bleeding. It's more common in the elderly and can be a source of significant blood loss.
Hemorrhoids: While often associated with painless rectal bleeding, hemorrhoids can cause discomfort and pain, especially if thrombosed. They are very common and should be considered in the differential diagnosis.

Mesenteric Ischemia: This is a life-threatening condition that requires immediate intervention. It can cause severe abdominal pain out of proportion to physical examination findings and can lead to rectal bleeding. The risk factors include age, atrial fibrillation, and other cardiovascular diseases.
Inflammatory Bowel Disease (IBD): Although less common in new diagnoses among the elderly, IBD (including Crohn's disease and ulcerative colitis) can present at any age and cause both abdominal pain and rectal bleeding.
Ischemic Colitis: This condition can cause abdominal pain and rectal bleeding due to decreased blood flow to the colon. It's a medical emergency and requires prompt diagnosis and treatment.

Intussusception: This is a condition where a part of the intestine telescopes into another part, which can cause abdominal pain and rectal bleeding. It's rare in adults but can be associated with a lead point such as a tumor.
Meckel's Diverticulum: A congenital anomaly of the small intestine that can cause bleeding due to the presence of ectopic gastric mucosa. It's rare and usually presents in younger patients but can be considered in the differential diagnosis of gastrointestinal bleeding.
Gastrointestinal Lymphoma: A type of cancer that can cause abdominal pain and rectal bleeding. It's less common than other gastrointestinal malignancies but should be considered, especially in patients with risk factors or systemic symptoms.