Miko = Mace Windu.
IMO, this whole scene is intended as a recasting of the Mace & Anakin confront Palpatine in Revenge of the Sith, with Shojo as Palps, Miko as Mace and Hinjo as Anakin. Obviously with a different background, outcome and right answer - but to me, the changes only serve to highlight the parallels (possibly even to make this scene a commentary on the one in Ep. 3?).
Mace was breaking the jedi code by attempting to strike down an apparently helpless Palpatine... = Miko is breaking the paladin code by striking down helpless Shojo...
... because he believed the Senate could or would not deal with Palpatine because he has corrupted them... = ... because she believes the magistrates could or would not deal with Shojo because he has corrupted them...
... as well as believing Palpatine is actually working in concert with the Separatists to achieve dictatorial control... = ... as well as believing Shojo is working with Xykon to achieve dictatorial control...
... while Anakin looks on in stunned horror as his mentor and friend, who he nonetheless was willing to condemn and deal with legally, is about to be executed. = ... while Hinjo looks on in stunned horror as his uncle and mentor, who he nonetheless was willing to condemn and deal with legally, is executed.
Now, the big differences are a) Palpatine is actually conspiring with the Separatists and is faking being helpless, whereas Shojo isn't guilty (presumably), b) Anakin stops Mace, whereas Hinjo doesn't (again, presumably - we don't *know* Shojo is dead), and c) Roy and Belkar are present as observers. However, R&B appear to be, for purposes of this scene, purely observers, completely removed from the action.