Environment here is rather different with the police commissioner. Nixon was seen as being far too cosy with the government, and was in a rather strong rivalry with the police union. Overland is in a similar position, and trying to distance himself from this in recent times, with slight criticism of the government in recent times.
I think that Nixon is seen by a large percentage as a political appointment, especially considering that she walked straight into the job after resigning.
Nixon's decision making seems completely in line with her organizational manner throughout. She was big on empowerment and delegation. It was credited with great progress in the early years of her time, and was a cause for much concern from the members of the police union in the later years, as paperwork and bureaucracy increased. It would appear that this is what shot her in the foot in this instance.