I had IBS as a teen, and it turned out to be low fiber intake, and it was easily fixed with more veggies. Potassium deficiency can make a digestive system do this, I've gone through that too. Can she drink plenty of water or diluted OJ so she gets plenty of liquids plus some potassium, if it works it's potassium/dehydration problems. Or I'd get her on fiber pills and try those as home remedies while waiting for testing/Dr. Appointments. I never needed to be put through the discomfort of a barium swallow test as as teen at all!
Welcome to the gastroenterology community! She needs to see a gastroenterologist about this and have some testing done to figure out what is wrong.