My cousin was sexually assaulted. How can I help her?

Be her friend. Don't try to be her therapist. Recovery will include making sense of the event, recognizing what is still intact, focusing on the future rather than the past, on how she can still love and be loved. If she's having intrusive memories or other PTSD-type symptoms, encourage her to get these treated -- we have interventions that work pretty well. I am glad you are there for her.