It's easier to write stories for a cliche (angry tough hot chick who just wants to get her kid back, blergh). But the benefit of not having a cliche character is that the writers might have to work harder to come up with stories, and the stories might be more imaginative.And yeah, why exactly was that blond lady replaced?
The fact that they changed the character to make their jobs easier does not say a lot about the ambitiousness of the writers on this show. Jimmi Simpson is pretty much just carrying it on his own.
My theory was the cast of crooks was to close to the Leverage team of crooks. The problem with the show is aside from the profiler that the Marshals Service gets for a cheap price nobody has a "super power" that any ordinary cop wouldn't have.