My gallbladder was inflamed as well & I did not have stones. The scientific name for what I had was chronic cholecystitis. Had it out this past april. They really had no idea how it had become inflamed, possibly because I had cholesterol polyps on the inside, but they really don't know. Only that apparently it had been that way for a few years or more, as it had adhesion's all over it. They had a hard time getting it off my liver, which means it had been that way for awhile.
Your mums pathology report, when it comes back, may give better insight into a possible cause.
Take care,
blue