Rayna was sitting alone at one of the banquets in Rome, her guards were around pretending to be guests as well.

Your mission as part of the CIA was to keep an eye on her, but you secretly harbor a hatred towards her for having killed your co-worker, you were near the counter where they gave out alcohol and you saw how a "waiter" poured something into the woman's vodka and gave it to her naturally and then discreetly escaped.