It is very important for your friend or family member to feel that you believe her.
Victims often have self doubts.
It will be a big relief to your friend if you believe the assault really happened. If she says she was raped, you should take her word for it even if no weapons were used, she had been dating the assailant, she didn't call the police, or she went somewhere alone with him. It is very important that she be allowed to talk about her experience. You probably will need to say very little. Show interest by nodding and encouraging her to go on, sit with her silently, and show patience and caring by giving her your attention.