C. NSAID induced HTN: The patient has been using NSAIDs to relieve her RA symptoms. NSAIDs are known to cause hypertension by inhibiting prostaglandin synthesis, leading to renal vasoconstriction and sodium retention. Given her recent history of NSAID use and the development of hypertension, this is the most likely cause.

A. Essential hypertension: Although less likely given her age and the presence of other potential causes, essential hypertension remains a possibility. However, her age and the absence of a long-standing history of hypertension make this less likely compared to NSAID-induced hypertension.
D. Primary hyperaldosteronism: This condition, characterized by excessive aldosterone production, can lead to hypertension and hypokalemia (low potassium levels). The patient's low potassium level (K+ 3.0) could suggest this diagnosis, but it would be less common and typically presents with more pronounced hypokalemia and metabolic alkalosis.

B. Pheochromocytoma: Although rare, pheochromocytoma is a critical diagnosis not to miss due to its potential for severe, life-threatening hypertension. It is less likely given the patient's presentation and lack of other suggestive symptoms (e.g., episodic hypertension, palpitations, sweating), but it should always be considered in the differential diagnosis of hypertension, especially in younger patients.

Renal artery stenosis: This could be a consideration, especially given her history of type-1 diabetes mellitus, which increases the risk of renal vascular disease. However, it is less likely and would typically require additional symptoms or findings suggestive of renal disease.
Cushing's syndrome: Another rare cause of hypertension, Cushing's syndrome could explain her hypertension but would typically be accompanied by other signs such as weight gain, moon facies, buffalo hump, and purple striae, which are not mentioned in the scenario.