In a novel in which many characters are trapped in a literal prison, it's a neat twist that there is no one who is truly free. Those who aren't confined by the law are trapped by their own stubbornness, the demands of their social circle, the rote boredom of everyday life, or an inflexible and harmful belief system. Imprisonment is certainly oppressive, but in Little Dorrit, "freedom" is almost as bad – a permanent state of waiting for the other shoe to drop.
Distressing as it may be, the only person who has truly broken away from the various bonds that imprison her is Miss Wade. She proves the novel's rule that freedom is not necessarily a good thing, but something that needs to be tempered with a reasonable amount of confinement.