It’s an odd situation. I would think it would be unusual for a visa to be denied after an “approval”. I hate to ask, but is it possible she was “less than forthcoming” about some detail and they found out? Do you know what rule she was denied under?
I don't know much... their reason is she's an "immigration risk". I have never met this kid (friend of my friends). She's just getting published and recognized in S.A. as a fitness model, and being young, she may have said something dumb like "I hope to get discovered somehow in my visit to the USA".
I'll get all the scoop next week when my friends do get here.