Community-Acquired Pneumonia (CAP): Given Valerie's symptoms of productive cough, worsening dyspnea, chest pain on coughing, and bilateral lower lung opacities on chest X-ray, CAP is the most likely diagnosis. Her history of COPD and morbid obesity may also predispose her to respiratory infections.

Exacerbation of Chronic Obstructive Pulmonary Disease (COPD): Valerie's history of COPD, symptoms of worsening dyspnea, and bilateral wheezes could indicate a COPD exacerbation, possibly triggered by an infection or other factors.
Pulmonary Embolism (PE): Although less likely given the presence of bilateral lower lung opacities, PE should be considered, especially in a patient with risk factors such as morbid obesity and possibly immobility.
Acute Bronchitis: This could be a consideration given the productive cough and bilateral wheezes, but the presence of bilateral lower lung opacities on the chest X-ray makes CAP more likely.

Influenza or Other Viral Pneumonia: Given the severity of Valerie's symptoms and the potential for rapid progression, especially in a patient with multiple comorbidities, it's crucial to consider and test for influenza or other viral causes of pneumonia.
Pneumocystis jirovecii Pneumonia (PCP): Although Valerie's immune status is not fully detailed, her history of DRESS syndrome and potential immunosuppression due to underlying conditions or medications makes PCP a diagnosis that should not be missed, especially if she is not responding to typical antibiotic therapy.
Tuberculosis (TB): While less common, TB can present with similar symptoms and should be considered, especially if there's a history of exposure or if Valerie does not respond to standard antibiotic therapy for CAP.

Cystic Fibrosis Exacerbation: Although Valerie's age and lack of mentioned cystic fibrosis history make this unlikely, it's a rare condition that could present with similar respiratory symptoms.
Eosinophilic Pneumonia: Given Valerie's history of DRESS syndrome, which involves an allergic reaction, eosinophilic pneumonia could be a rare consideration, especially if there's an atypical response to standard treatments.
Lymphangitic Carcinomatosis: This rare condition, which involves metastatic cancer spreading to the lymphatics of the lungs, could present with similar symptoms but would be less likely without a known history of cancer.