Spark has not yet been seen.
Taravangian states that, with regard to Spark, he and Malata need to be cautious because they can't be certain as to what Spark will do as her self-awareness grows. He says that she will surely dislike working against the other orders of Knights Radiant.
Malata responds that Spark is fine with what they are doing. That she is game for whatever it takes to get vengeance for how organized devotion to Honor killed hundreds of ashspren. And to whatever lets her break stuff.