I wouldn't at this time. It may be good for you, but interestingly enough the lemon may be a bit harsh for the 5 yr. old. While it is possible she could have gallbladder issues, at her age it would be only sand. It would also suggest that others in the family tree have had similar issues, i.e. heredity.
While I don't know about what you can do about her brain and tummy, which I think in child speak is upset stomach, but its hard to tell isn't it? Kids are very sensitive to things, how long has she be saying this? You might consider an ultrasound for her, they will check the liver/gallbladder/pancreas/common bile ducts, just to make sure. Give her candies before and treats afterward to she focuses on that. Smile. Maybe send a sample of her stool of for testing, she might have parasites, kids eat the strangest things. You can also take a sample of her saliva and hair to a natural path for testing to see if she is deficient in anything. Best of luck.