agree with the above. university of chicago has some experience with this. search helen te on pubmed for some literature background.
For a start , you can find the survival rates for combined heart and liver transplants (CHLTx) for 1, 5, and 10 yrs, at the Mayo Clinic in an article entitled Combined Heart and Liver Transplantation: A Single-Center Experience. Survival rates for the CHLTx recipients at 1 year, 5 years, and 10 years were 100%, 75%, and 60%, respectively, and did not differ from survival after isolated heart transplantation (93%, 83%, and 65%), respectively. http://journals.lww.com/transplantjournal/Abstract/2009/07270/Combined_Heart_and_Liver_Transplantation__A.11.aspx
Good Luck to your sister!