Not for me, within hours of my operation my usual ability to eat everything that wasn't nailed down, was restored, but then I am naturally greedy.
But, it is a major op and I couldn't get over how exhausted and limp I felt for weeks. So, you mother may easily have picked up a bug and will be not have any energy to fight any infections off. If she is still in hospital then they should be treating her, if she is back at home, I think she should seek an appointment with her GP.