I'm a graduate student in speech-language pathology, and this girl's case sounds very much like a disorder called achalasia that was recently discussed in my dsyphagia class. It's not psychological; it's caused by the failure of the lower espohageal sphincter to relax, which means food can't pass from the espohagus to the stomach, leaving it nowhere to go but up and out. It's often misdiagnosed as an eating disorder, and can go undiagnosed for many years.