I had the same mystery 28 years ago with my toddler... it turned out to be the grape juice he was drinking too much of.
any upper right quadrant pain, has she been ingesting any blue colored drinks foods or dyes , any pain in any part of abdomen, fever, or constipation?
it could be salmonella, or she could have a case cholecystitis, or cholelithiasis(gallbladder disorders) how old is she, what does she eat, is she overwheight, underwheight, what does she eat a lot of, did she eat any abnormal foods the day before it started happening
there is no new vitamin or food change to explain