Even before Arya killed the Night King, a lot of people thought she'd be the one to end Cersei. Cersei has been on her list for a long time, and Arya was on her way to kill her before deciding to head home to Winterfell after she learned Jon was there.
To tie in with the valonqar prophecy, some fans think Arya will take Jaime's face and kill Cersei while wearing it. But that would probably require Arya killing Jaime too, which I don't think will happen at this point. He seems pretty firmly embedded in Team Stark after the Battle of Winterfell – although who knows, maybe Bran will spill his tea and the Starks will turn on Jaime again.
Still, giving Arya BOTH major kills of the season doesn't seem like something the showrunners would do.