Ovarian Cancer: This is the most likely diagnosis given the patient's symptoms of abdominal bloating, early satiety, increased abdominal girth, and imaging evidence of a pelvic mass with peritoneal spread. Ovarian cancer is known for its non-specific symptoms until late stages and often presents with spread to the peritoneum.

Uterine Cancer: Although less common than ovarian cancer with these specific symptoms, uterine cancer can also present with a pelvic mass and spread to the peritoneum, especially in postmenopausal women.
Gastrointestinal Cancer (e.g., Gastric or Colorectal Cancer): These cancers can metastasize to the peritoneum and cause similar symptoms, including abdominal bloating and early satiety, though they are less likely to present as a primary pelvic mass.

Lymphoma: Although less common, lymphoma can present with abdominal symptoms and a mass, and it is crucial not to miss this diagnosis due to its different treatment approach and potential for cure with early detection.
Tuberculous Peritonitis: This condition can mimic peritoneal carcinomatosis and is important to consider, especially in endemic areas or in patients with risk factors for tuberculosis, as it requires a different treatment approach.

Primary Peritoneal Cancer: This is a rare cancer that arises from the peritoneum itself and can present similarly to ovarian cancer, with abdominal bloating, ascites, and a pelvic mass.
Pseudomyxoma Peritonei: A rare clinical syndrome characterized by recurrent mucinous ascites causing abdominal distension, often associated with a primary mucinous tumor of the appendix.
Mesothelioma: A rare cancer of the peritoneum that can cause similar symptoms, including abdominal bloating and a mass, though it is more commonly associated with asbestos exposure.