The antibiotics are a good first line treatment, and definitely follow up with the liver enzymes. From what I could find,
IBS could
cause swollen lymph nodes, so if her IBS is flaring up, maybe that is the cause. I would think that they might want to do an abdominal ultrasound to see what is going on with her liver. Sometimes, with an acute infection, liver enzymes can be elevated. I would recommend your sister continue her follow up with the infectious disease doctor.