**Core Concept:** The question involves understanding the clinical features and diagnostic findings of an autoimmune disorder called Coeliac Disease, which is characterized by an immune response against dietary gluten proteins, leading to villous atrophy and malabsorption. In this case, subepithelial bullae with granular IgA deposits on basement membrane are characteristic histopathology findings in Coeliac Disease. Gluten sensitivity is a broad term for reactions to gluten, but here it highlights the association with the disease.

**Why the Correct Answer is Right:**

The correct answer is **C. Coeliac Disease**. This diagnosis is supported by the presence of subepithelial bullae with granular IgA deposits on basement membrane, which are characteristic histopathology findings in Coeliac Disease. IgA is an immunoglobulin that is deposited in response to gluten antigens. Additionally, the patient has some degree of gluten sensitivity, which is a common feature in Coeliac Disease.

**Why Each Wrong Option is Incorrect:**

A. **Celiac Sprue**: Although a correct answer, it is an older term for Coeliac Disease. Given the question, we prefer to use "Coeliac Disease".

B. **Lupus**: Lupus is a systemic autoimmune disease with different clinical features and histopathology. The presence of granular IgA deposits on basement membrane is specific for Coeliac Disease and not a feature of Lupus.

D. **IgA Nephropathy**: IgA Nephropathy is a kidney disease associated with IgA deposition and should not be confused with Coeliac Disease. The histopathology features are different, and IgA deposition is not a hallmark of Coeliac Disease.

**Clinical Pearl / High-Yield Fact:** Gluten sensitivity is not specific to Coeliac Disease and can be seen in other conditions like Lupus or IgA Nephropathy. However, the presence of subepithelial IgA deposits on basement membrane along with the clinical context of gluten sensitivity is highly suggestive of Coeliac Disease.

This question highlights the importance of considering the clinical context, histopathology findings, and a high index of suspicion when evaluating a patient with gluten sensitivity. It also emphasizes the need to differentiate between similar-sounding conditions like Lupus and IgA Nephropathy, which have different clinical and histopathology features.