Sorry to hear for your mum's condition!
Was she treated for the primary cancer?
Is only one area of the liver affected?
What other symptoms she has?
Feeling tired is a common side effect of liver problems because one of the responsibilities of the liver is to store carbohydrates, allowing for a quick release of energy when necessary.
When your liver is not working well, its ability to store this energy is not effective, creating feelings of lethargy.
Also, fatigue is the most common side effect of cancer itself and its treatment.
About 90% of patients experience fatigue during and after chemotherapy or radiation.