It is essential that they know they are believed, and that they be allowed to begin to rebuild their life at their own pace. People who have been raped or sexually abused need to rebuild feelings of safety, trust, control and self-worth, all things which are often lost through an assault. The responses of those near to a survivor can occasionally make things more difficult for him or her, and that is something nobody wants. The focus should always be on the survivor - never try to make them do anything they don't feel comfortable with. Also try to remember that you need support too, in order to continue supporting the survivor.
Counseling is available for secondary survivors too.
Anybody, anywhere, can be a victim of abuse, regardless of age, gender, looks, dress and so on. Any criticism of their handling of the situation, either during the attack or afterwards, simply adds to that guilt, and it is important that the blame is placed firmly where it belongs - with the person who committed the assault. Do Understand Listen and try to understand why they were unable to prevent it from happening. They may have been frozen by fear, or have been unsuspecting and trusting, or they may have been threatened or physically attacked and may have realistically feared worse would happen if they resisted. You wouldn't expect somebody who has been mugged to have been able to prevent it.