Diverticulitis: This condition is a common cause of lower left quadrant (LLQ) abdominal pain, especially in older adults. The pain is typically constant and can be accompanied by changes in bowel habits, fever, and nausea. Given the patient's age and the location of the pain, diverticulitis is a strong consideration.

Irritable Bowel Syndrome (IBS): While IBS can cause a variety of symptoms including abdominal pain, it is less likely to cause severe, localized pain in the LLQ. However, it's a common condition and should be considered, especially if the pain is chronic and accompanied by changes in bowel habits.
Constipation: Constipation can cause significant abdominal pain and is common in older adults. The pain can be localized to the LLQ, especially if there is a significant amount of stool in the sigmoid colon.
Ovarian Cyst or Torsion: Although less common, ovarian cysts can cause LLQ pain, especially if they rupture or torsion occurs. This is more likely in premenopausal women but can occur in postmenopausal women as well.

Appendicitis: Although appendicitis typically causes right lower quadrant pain, it can occasionally cause LLQ pain if the appendix is retrocecal or if the patient has an atypical anatomy. Missing appendicitis can lead to severe consequences, including perforation and peritonitis.
Ectopic Pregnancy: While less likely in a 58-year-old female, ectopic pregnancy can still occur, especially with the use of fertility treatments. It is a life-threatening condition that requires immediate attention.
Intestinal Obstruction: This can cause severe abdominal pain, vomiting, and constipation. It requires prompt diagnosis and treatment to prevent complications like bowel ischemia.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis can cause chronic abdominal pain, diarrhea, and weight loss. While not immediately life-threatening, missing IBD can lead to significant morbidity.

Endometriosis: While endometriosis is more common in younger women, it can still occur in postmenopausal women, especially if they are on hormone replacement therapy. It can cause chronic pelvic pain, including LLQ pain.
Colonic Neoplasm: Colon cancer can cause abdominal pain, changes in bowel habits, and weight loss. While not the most common cause of acute LLQ pain, it is an important consideration in the differential diagnosis of chronic or persistent symptoms.
Inferior Mesenteric Artery Embolism: This is a rare but life-threatening condition that can cause severe abdominal pain. It is more likely in patients with atrial fibrillation or other sources of emboli.