If she doesn't report it, the guy is free to do it again and again and again. If she does report it, she will gain a certain sense of having done something about it, taking some power over her life back, and not just a little revenge on him.
She absolutely needs to report that she was robbed as well. There is an important distinction with sps vs civilians, and that is the sex is consensual based on payment. She could also look up the info for PIVOT, and may be able to take someone with her to make the report so she doesn't feel alone. An advocate to help her thru the process, and to make sure it is all taken seriously can help.