This is just getting bad, she is completely processing things, her vision was alright, she was consciously thinking about things, she even felt stuff, I don't know why we are making assumptions of her being dazed in the first place, but alright, I guess.
Either way, being dazed or not, sensing is not related with processing information, she just needs to sense the sound and tell the reader about it.
She didn't even react to the sound, reacting to sound would be doing some movement or generating a response in response to the sound. Like if someone were to scream right behind your ear, you would get scares and jump from your place, that jumping from your place is what is reaction, again, I get you are still using the fact of her reacting to sound as a thing, reaction and sensing is different.
The thing is, the smack happened only once, so how is she even hearing the sound later?
She literally just needs to sense the sound and tell the reader about it, that is enough, or more than enough to tell that there was a delay in sound.