In A Clash of Kings, after Jaqen H'ghar has finished his tasks for Arya he gives her a coin and tells her a phrase: "Valar Morghulis"
Fast forward to A Storm of Swords. When Dany "buys" her unsullied from Astapor, they give her a translator (since they don't know she actually speaks Valyrian) who Dany subsequently frees. The translator, however, agrees to travel with Dany despite the danger. The interaction goes something like
"Valar Morghulis", "Indeed everyone must die"
so we learn that "Valar Morghulis" translates to "everyone must die."
Now, a few chapters later when we get back to Arya she comes upon some northmen caged up in the city. The men are dying of thirst and Arya gives them water (before they are shot by Anguy). After giving them water, they are shot with arrows to the throat and Arya mutters
My question is, does Arya somehow know the meaning of these words at this point? Or is it just coincidence she said them at this time?