That's a hell of an easy Google Image search. Either she didn't think to take credit for a halfway decently hidden picture, or she drew it.
So far, I only know that Soze is intelligent, artistically capable, and that she has no known record of dishonesty. I'm gonna say that right now, I believe her.
That said, I also have no reason not to contact the Pepsi Lady to see if she 1. owns the picture in question, or 2. knows where it came from if it isn't hers. If all goes well, she can confirm aspects or the entirety of her story. Should she know the school's name, I will respect Soze's privacy and not name it.