If her bile ducts are blocked, then her alkaline phosphatase (Alp) will be elevated. If the bile flow is mostly or completely blocked, then her Bilirubin level will be elevated and she will likely have dark urine, floating stools and possibly jaundice, if her Bilirubin levels are higher than 2.5 mg/dL.
Sludge can be an indication of biliary issues. However, simply following an extreme diet will few meals can cause it as well. But enough sludge will be noticable as RUQ aches and mild nausea with low grade fevers.
If you remain suspicious of the possibility of some form of gallbladder/biliary issue, then press her doctor for an MRI/MRCP. It is the best image technology for this type of thing. I have had many myself, and if you have biliary issues, this will show the pathology very well.
Good luck and hope things get straightened out. Take care.