Diverticulitis: Given the patient's history of colonic diverticulosis and symptoms of intermittent severe abdominal pain, diverticulitis is a highly plausible diagnosis. Diverticulitis occurs when diverticula in the wall of the colon become inflamed, which can cause severe abdominal pain, changes in bowel habits, and other symptoms.

Exacerbation of Ulcerative Colitis or Crohn's Disease: The patient's history of ulcerative colitis/Crohn's disease makes an exacerbation of the underlying condition a likely cause of her symptoms. Both conditions can cause intermittent abdominal pain, among other symptoms.
Irritable Bowel Syndrome (IBS): Although IBS is more chronic and less likely to cause severe pain, it can sometimes present with intermittent severe abdominal pain, especially in patients with a history of inflammatory bowel disease.
Intestinal Obstruction: Given the patient's history of colonic diverticulosis and inflammatory bowel disease, there is a possibility of intestinal obstruction due to adhesions, strictures, or other complications.

Appendicitis: Although less likely given the patient's symptoms and history, appendicitis can present with intermittent pain and must be considered due to its potential for severe consequences if missed.
Ovarian Torsion or Other Gynecologic Emergencies: These conditions can cause severe, intermittent abdominal pain and are critical to diagnose promptly to prevent serious complications.
Bowel Perforation: A perforation of the bowel, which could be a complication of diverticulitis, ulcerative colitis, or Crohn's disease, is a medical emergency that requires immediate attention.

Meckel's Diverticulum: A congenital anomaly of the small intestine that can cause abdominal pain, bleeding, or obstruction, but is less common and typically presents at a younger age.
Intussusception: A condition where a part of the intestine slides into an adjacent part, which can cause intermittent abdominal pain and is more common in children but can occur in adults, often associated with a lead point such as a tumor.
Ehlers-Danlos Syndrome: A group of disorders that affect connective tissues supporting the skin, bones, blood vessels, and many other organs and tissues, which can lead to gastrointestinal symptoms including abdominal pain, although it is a rare condition.