Aishi was looking for justice. Given what we see of the state of authority in the Jade Empire, where the Lotus Assassins are basically trying to shunt the Imperial Army to guarding fish markets, where a man like Sen, who speaks openly about Fading Moon not being a concern until her arson moved out of the poor districts and into those of money, where we have judges who are looking to throw an innocent scholar into jail and let a slaver go free... Justice wouldn't come at the hands of any authority of mortals. Someone would probably have bailed him out - after all, a man like that rose to prominence in the first place.
I love this quest. Hell, my first time through, I legitimately found myself wishing I could recruit Aishi to help her atone or something. A lot of it has to do with her voice actress's performance. I'm still hoping that BioWare taps her for a companion character in the future (since she had recurring roles as the asari councilor and Doctor Michel, I'm hopeful for Andromeda.)