Right now the best thing to do is nothing, you don't want to use anything that will stimulate the immune system. If you do, you might have her immune system working so well that it has a problem accepting the liver transplant.
Maybe a little Total Toddy would be alright, but only under a Doctor's supervision. You'll need to ask her physician when it would be alright to start a supplementation program again. Some people could begin as early as a month after the transplant and some may need to wait a year before for the body to normalize with the presence of the new implant. Best wishes to your mother in her transplant.