Your compassion and listening skills are very important for your friend. One year is not a long time at all to get through grief especially with the death of a sibling. She will benefit by sharing memories of her sister and finding ways to keep those memories alive. Holidays, birthdays and anniversary dates of the death will always be more potent reminders. Finding ways to memorialize her at these times help. It is good to know that she does have a close friend who understands her. We can never really "know" what someone is actually going through.