In fact, she didn't mistake several things. She didn't make any mistake, but she didn't remember date and time. Which is normal, because dates and times are not objects for the memory, people often don't know what date is today (they may ask it) and often don't take note of the time.
But she remembered very well the scream. It is not reasonable to assume she had mistaken the scream. Sorry, but this is really not reasonable. You have infinite occasions to be uncertain about the date, but you won't make a mistake on hearing the desperate scream of a woman. I'm not talking of a "mistake" on time like Amanda's, who says "the only thing I am certain about is that we had dinner late". Nara a is really uncertain on the date number (1..2..), and about things happened in days around, but not on the day: that scream was on the night of the murder.
I wonder how you could even figure out this "mistake" of hearing a terrifying scream that dosn't happen.
Moreover, I wonder why you forget to put weight on Antonella Monacchia's testimony who speaks about the same night, to draw your conclusions.