When I had an ICD implanted, I was purple from my shoulder down my side to my hip for, at least, 3 weeks, probably 4. My back and front were also bruised. I also had a burning sensation and sometimes still do, even though it's been several years. Her heart might be feeling like it's beating really fast but has anyone ever actually checked it? If she was very accustomed to a really slow heart rate, it could feel extremely fast even though it's normal. If it really is high, she should see the cardiologist. Also, she may not be walking because of the soreness but I would think her doctor would want her to walk because that will helps heal. If she stays tired and not walking, I would call the cardiologist on that also.
They had to create a pocket to place the pacemaker into. It's a rather "wet" surgery, meaning blood loss and plasma seepage into the area.