The chances of Arya killing Cersei are pretty low especially if its the FM sending her. She knows her they know about her list and who is on it and there is the whole valonqar prophecy about Cersei dying to either tyrion or jaimie after losing her kids.
Plus really this is how I see it by the end of the book
Jon - AA reborn, becomes king, fights others
Bran - Bloodravens successor, all knowing and extremely powerful godlike status
Sansa - Learns from littlefinger becomes one of the best at the game rules over the vale and/or riverlands
Rickon - Lord of Winterfell (he isnt a major character anyway)
Tyrion - takes over casterly rock and or becomes dany's hand, maybe becomes a dragon rider
Dany - helps fight others might be jons queen
Arya - runs around in the riverlands for the first half of the series, becomes one of the best killers in the world and ends up killing Cersei who is already out of power and about to lose to Dany or Aegon or Jon anyway, or she kills some Freys and boltons who are in the same situation.
Nah she has to have a bigger end game