The purpose of the machine is to take care of an infant. the robot's equipped with a lullibye, a whistling toy, a bottle of milk and a metal belt. She can also change a baby's diper, and has the proper equitment and protocol to do so. She also has a calm, soothing voice.
The Robot Nurse Maid cannot define if one is or is not a baby, and therefor mistakes Donald Duck for an infant and treats him like one.