I'm so sorry to hear this...
I work for a criminal justice agency, in part writing materials about crime statistics that I provide to victims' advocacy centers. It is very important your SIL finds help and counseling through one of these centers. While family may be of comfort to her, these programs can provide her with information and she will have people to speak to who KNOW exactly how she is feeling.
There is a lot involved in this whole process, and sometimes it is difficult not to feel like the victim is being further injured by the invasiveness of rape exams, prosecution of the offender, etc... She needs to seek expert counseling as soon as possible.