Fordola was not only in command but also did some bad things towards innocent people. Her group beat up those that could not pay, which we saw with our own eyes. She then did something really heinous by bascially shooting at her own soldiers/friends. Who knows what else she did in all those years.

Unlike her, many Garlean soldiers just did what they were told to do. We also have to remember that a lot of them were conscripts who might not even want to fight. We have heard what will happen to the families of such soldiers if they refused to take up arms.

So there is quite a difference between someone like Fordola who also took it out on civilian and the common soldier who might have just fought against other soldiers.

In the end Fordola only got the collar (thus a chance at life) because she was useful with her echo otherwise she would have been killed.