Below is a sentence I found in Longman Dictionary of Contemporary English. Could you please explain why the adjective "incredulous" is used as if it's an adverb?
'You sold the car?' she asked, incredulous.
Should it be amended to include "incredulously" and exclude the comma:
'You sold the car?' she asked incredulously.
P.S. I appreciate the possibility that this is a common structure, as opposed to being unique to "incredulous", yet I'm just not familiar with such a structure.