This is the 205th most frequent Croatian word.
potpuno
Completely.
Here, "potpuno" is used as an adverb to emphasize the completeness of her readiness.
Ona je potpuno spremna za ispit.
She is completely ready for the exam.
In this case, "potpuno" modifies the adjective "neočekivan" to stress the extent to which the answer was unforeseen.
Njegov odgovor bio je potpuno neočekivan.
His answer was completely unexpected.
Here, "potpuno" acts as an adverb to indicate the full extent of understanding.