Friend saw grandma choke to death infront of her. she can't forget the image it haunts her. refuses to tell parents, says they won't care. what to do?

Silent sufferer: Your friend is likely suffering from Post Traumatic Stress Disorder. Would suggest seeking out Grief or Trauma counseling. There are even support groups where others can get together and process the feelings and loss. If symptoms are causing major difficulties for you friend encourage them the seek medical attention as there are medications that have indications to treat PTSD