Choledocholithiasis: Given the patient's history of cholecystectomy and the presence of dilated intrahepatic and extrahepatic bile ducts on imaging, along with elevated liver enzymes, choledocholithiasis (stones in the common bile duct) is a highly plausible cause of her symptoms. The recommendation for MRCP and the decision to proceed with ERCP further support this diagnosis, as these procedures are commonly used to diagnose and treat bile duct stones.

Bile Duct Stricture: This could be a complication from her previous cholecystectomy or a result of chronic inflammation. The dilatation of the bile ducts suggests an obstruction, which could be due to a stricture.
Hepatitis: Although her hematology is unremarkable, the significant elevation in AST and ALT suggests hepatitis, which could be drug-induced (given her medication list) or viral.
Drug-Induced Liver Injury: Given the patient's extensive medication list, drug-induced liver injury is a possibility. Drugs like methimazole, ezetimibe, and others can cause liver enzyme elevations.

Cholangitis: Although the patient does not have the full classic Charcot's triad (fever, jaundice, and abdominal pain), cholangitis is a serious condition that requires prompt diagnosis and treatment. The presence of bile duct dilatation and elevated liver enzymes makes this a critical diagnosis not to miss.
Hepatic Artery Thrombosis: This is a rare but potentially life-threatening complication, especially in the context of recent surgery or in patients with hypercoagulable states. The patient's atrial fibrillation increases her risk of thrombotic events.
Liver Cancer: Given the patient's age and the presence of significant liver enzyme elevations, although less likely, liver cancer should be considered, especially if there are risk factors not mentioned (e.g., hepatitis B or C, alcohol use).

Primary Biliary Cholangitis (PBC): An autoimmune disease of the liver characterized by progressive destruction of the bile ducts within the liver. It's less likely given the acute presentation but could be considered in the differential for chronic liver disease.
Primary Sclerosing Cholangitis (PSC): A chronic liver disease characterized by inflammation and scarring of the bile ducts inside and outside the liver. It's rare and often associated with inflammatory bowel disease, but it could explain the bile duct dilatation.
Budd-Chiari Syndrome: A rare condition caused by occlusion of the hepatic veins or the inferior vena cava. It could present with abdominal pain and elevated liver enzymes but is less likely without specific risk factors (e.g., thrombophilia).