You didn't say what kind of liver damage your sister has, so it's hard to offer anything specific here. For someone to have such a serious condition, it obviously has been a long time in development and would require many dietary and lifestyle changes. She should be eating completely processed-free, and will probably require juicing, supplements, and lots of rest.
Most information I found in my literature suggest that the liver is the real underlying cause and that measures should be taken to cleanse and heal the liver. If you don't already know about Dr. Sandra Cabot, you should check out her website at http://www.liverdoctor.com.
She is an expert on liver health, and your sister should read as much information as she can on that site.
I also found this website that offers some information about treating an enlarged spleen:
And on another website I found this info:
Enlarged Spleen Natural Treatment
In the treatment of Enlarged Spleen natural remedies can be quite effective in providing relief from discomforting symptoms. These natural Enlarged Spleen remedies are
Lemon Juice Mixture
Mix 10 ml lemon juice with 6 ml of onion juice and consume the mixture daily in the morning and evening. This can help cure the condition.
Soak 5 date fruits overnight in a glass of water. Churn the mixture in the morning, add half teaspoon full of raw honey to it and drink it.
If properly treated in time, an enlarged spleen can be cured with least complications and the sufferer can get back to health in a short time.
Please understand that these remedies were found on the internet and therefore no one knows whether they really work. I certainly am not making any claims, I just wanted to reply to your call for help. Your sister needs to see a naturopathic doctor or homeopathic doctor, someone who can make sure that the correct treatment is taken. Again, since you didn't say what kind of liver damage your sister has, no definitives can be made. Please read everything very carefully, and your sister should be reading everything as well. She needs to be the one who is educated, and you can be her support.