Conclusion
Most exhibitionists in situations like Sue's blond man would never get in touch with the girl they're showing off to, and in some ways, I think that Sue experienced something rare. Usually, if a man is going to expose himself out a window, it is because he's too scared to approach a girl on any other level.
It took Sue's man two whole weeks before he felt safe enough to send her the photo with his phone number, and I think that she handled everything in a rather adult manner. The book she was reading at her sister's, explaining various aspects of sex and its variations, surely helped her come to grips with the man across the alley, so much so, that even though she was a bit frightened, she still had the nerve to go over there.
It was beneficial to Sue, also, for the man obviously taught her enough good things about sex to make her want to go back to the city. As she left my office, she waved goodbye and told me that she'd send me a letter if anything new develops.