Is she avenging Sayaka, or just recently murdered her with her own sword?

Artist said:
こいつは私が仕留める

この魔女は斬撃で倒すしかないの　まどかは、さやかのそばにいて

"I'll take this one down.

This witch can only be defeated with a blade. Madoka, you stay with Sayaka."

Thanks for the clarification.

Still a deadly blow to Sayaka's ego if Homura manages to defeat a Witch vulnerable only to blades when the blademaster of the team couldn't...