Urinary Tract Injury or Bladder Dysfunction: Given Cheryl's history of a broken pelvis and the use of internal and external catheters during her hospitalization, it's possible that she may have suffered a urinary tract injury or developed bladder dysfunction, leading to her symptoms of urinary incontinence, urgency, and frequency.

Kidney Infection (Pyelonephritis): Although the urine culture was negative, it's possible that the infection may not have been caught or that the symptoms are due to a non-bacterial cause. The bilateral back/flank pain and worsening symptoms over the past three days support this diagnosis.
Irritable Bowel Syndrome (IBS) Exacerbation: Cheryl's history of IBS and recent flare-ups suggest that her gastrointestinal symptoms may be related to an exacerbation of her IBS, possibly triggered by stress, changes in diet, or other factors.
Musculoskeletal Pain: The worsening back pain, especially on the right side, could be related to musculoskeletal strain or injury, particularly given her history of a broken pelvis and recent hospitalization.

Kidney Stones: Although Cheryl denies a history of kidney stones, it's essential to consider this diagnosis due to the severity of symptoms it can cause. The absence of radiating pain down her legs or nausea/vomiting does not rule out kidney stones.
Spinal Epidural Abscess: This is a rare but potentially life-threatening condition that can cause back pain, urinary retention, and other neurological symptoms. Given Cheryl's recent hospitalization and catheter use, this diagnosis should be considered.
Sepsis: Although Cheryl denies fever, chills, or body aches, sepsis can present atypically, especially in older adults or those with underlying medical conditions. It's crucial to monitor her closely for any signs of sepsis.

Cauda Equina Syndrome: This is a rare condition that can cause back pain, urinary retention, and bowel dysfunction due to compression of the cauda equina nerves in the spinal cord. Given Cheryl's history of a broken pelvis, this diagnosis should be considered, although it is less likely.
Neurogenic Bladder: This condition can cause urinary incontinence, urgency, and frequency due to nerve damage affecting bladder function. Although rare, it's possible that Cheryl's symptoms could be related to neurogenic bladder, particularly given her history of trauma and catheter use.