Stevens Johnson is a milder version of a condition called toxic epidermal necrolysis, and this looks severe enough to be the full-blown condition. Toxic epidermal necrolysis happens when a person takes any of a wide variety of ordinary medications (antibiotics, OTC cold medicines, almost anything) and the body reacts to the substance and decides to get rid of it. It gets rid of it by depositing it in the skin, except that then the offending substance is trapped in the skin and the immune system attacks and kills the skin trying to get rid of the stuff. Patients lose almost all their skin and are basically treated as burn victims. The really alarming thing is that nobody ever knows what might set it off... it can certainly kill you if your skinless body gets an infection. People even lose skin inside the mouth, in the throat, and from the surface of the eyes. It is probably top of the list of horrific random things you do not want to get.
I watched a show on discovery health about a woman that got stevens johnson syndrome from an antibiotic and she looked very similar to this girl. So..yeah...it CAN be that bad.