What Causes Swelling In Face And Neck Post Endoscopy And Colonoscopy?

My sister had an endoscopy and colonscopy. In recovery her face and neck started to sell. They treated her for allergic reaction to meds.... No help. They've done an MRI, and two barium tests looking for a tear. There is none. What has caused this? It occurred two days ago. Looks a little better but still swollen. ??