My 9 Year Old Daughter Had A Severe Reaction To

My 9 year old daughter had a severe reaction to her flu shot which included lal the symptoms you could think of PLUS green vomit. Urgent care treated her with anti nausea tablets. A follow up with her doctor lead to her being sent for upper GI testing. The doctor mentioned a twisted? gall bladder. I looked it up on line and this doesn't make sense to me. What could the doctor be testing for. I will follow up with the doc but I'm curious now.