Iron Deficiency Anemia (IDA): The patient's low iron level (20), elevated total iron binding capacity (TIBC) (130), and low hemoglobin (10) are indicative of iron deficiency anemia. The patient's symptoms of general weakness, shortness of breath (SOB), and pallor of conjunctivae also support this diagnosis. The fact that she has Crohn's disease, a condition known to cause chronic blood loss and malabsorption, further increases the likelihood of IDA.

Anemia of Chronic Disease (ACD): Given the patient's Crohn's disease, ACD is a possible diagnosis. However, the presence of low iron and high TIBC suggests that IDA is more likely. ACD typically presents with low iron, low TIBC, and elevated ferritin.
Vitamin Deficiency Anemia: Although less likely, vitamin deficiency (e.g., vitamin B12 or folate deficiency) could contribute to anemia, especially in a patient with Crohn's disease who may have malabsorption. However, the patient's MCV (84) is within the normal range, making this less likely.

Gastrointestinal Bleeding: Although the patient is on mesalamine, which can help control Crohn's disease symptoms, it's essential to rule out ongoing gastrointestinal bleeding as a cause of anemia. This could be due to uncontrolled Crohn's disease, ulcers, or other lesions.
Sepsis or Infection: Patients with Crohn's disease are at increased risk of infections and sepsis, which can cause anemia and other systemic symptoms. It's crucial to evaluate for signs of infection or sepsis.

Sideroblastic Anemia: This rare condition is characterized by abnormal iron metabolism and can present with anemia, low iron, and elevated ferritin. However, it is less likely given the patient's clinical presentation and laboratory results.
Pure Red Cell Aplasia: This rare condition is characterized by a failure of red blood cell production in the bone marrow. Although it could explain the patient's anemia and low reticulocyte count, it is less likely given the patient's other laboratory results and clinical presentation.