You can't have it both ways. The company didn't follow the correct process, so your friend has the job back again. You could most likely have asked for compensation instead of the job back, but its too late for that now.
Depending on what 'management' is doing to make life 'unbearable', her only option in terms of now extracting money is to resign and try and claim constructive dismissal - as Factor is suggesting.
But it is a high risk strategy. It depends what 'management' has been doing.