Ovarian cyst or tumor: Given the description of a large rubbery mass in the RLQ, which is a common location for ovarian pathology, an ovarian cyst or tumor is a highly plausible diagnosis. The dull pain associated with it also aligns with symptoms often reported by patients with ovarian masses.

Uterine fibroid: Although less common in the RLQ, a large uterine fibroid could potentially present in this manner, especially if the fibroid is pedunculated and has torsioned or is located in a position that refers pain to the RLQ.
Intestinal or mesenteric cyst: These can present as large, rubbery masses and could cause dull pain, depending on their size and location.
Lymphoma or other lymphoproliferative disorders: Enlarged lymph nodes in the mesentery or retroperitoneum could present as a large mass in the RLQ, though they might not typically be described as "rubbery."

Appendiceal mass or abscess: Although the pain is described as dull and 4/10, which is not typical for acute appendicitis, an appendiceal mass or abscess could present with a palpable mass in the RLQ and should not be missed due to the potential for serious complications if not treated promptly.
Ectopic pregnancy: In women of childbearing age, ectopic pregnancy is a critical diagnosis to consider, even though the presentation might not be typical. A large mass could potentially be a ruptured ectopic pregnancy, which is a medical emergency.
Torsion of an ovarian cyst or tumor: This condition can lead to severe pain and is an emergency. The initial presentation might be less severe, making it crucial not to miss this diagnosis.

Retroperitoneal sarcoma: These are rare tumors that can present as large masses in the retroperitoneum, including the RLQ.
Gastrointestinal stromal tumor (GIST): Although more commonly found in the stomach, GISTs can occur in the small intestine and present as a mass in the RLQ.
Desmoid tumor: A type of benign tumor that can occur in the abdominal wall or intra-abdominally, potentially presenting as a large, firm mass.