Final answer:
The situation exemplifies the ethical principle of justice, which involves distributing medical resources fairly and ensuring equal access to healthcare services for all individuals.
Step-by-step explanation:
The ethical principle that this situation exemplifies is justice. In this case, the mother meets certain criteria to be eligible for a liver transplant and understands that she is next on the waiting list for a donor liver that matches. Justice in healthcare involves distributing medical resources fairly and ensuring equal access to healthcare services for all individuals.