Hello and welcome to e health forum.
From the description provided , it seems that your mother may have a Infected Appendix with rupture, with resultant Abscess formation.
In conditions like appendicitis, oral intake of food, is not allowed. Nutrition is provided via IV fluids during this stage.
Keeping your age and medical status of your mother in mind, your doctors might be trying a conservative approach to treat the condition with antibiotics and supportive therapy.
In cases where the condition is diagnosed late, and the appendix ruptures, the surrounding structures including the omentum and intestines get adherent to it (felt as a lump). During this period, surgery is risky unless there is pus formation evident by fever and toxicity or by imaging studies. Conservative Medical management is more often used in such condition.
Once the medications have contained the infection, and there is improvement in your mothers ability to withstand the surgery, surgical treatment might be initiated.