Once Three-Dog is dead, you're stuck with Margaret. She also never appears in person and, therefore, cannot be killed. It seems like she doesn't enjoy her new announcing duties for the station. Margaret doesn't have a charismatic personality and has very little to say. Many players of the evil persuasion know you can kill Three-Dog (the DJ) and he will be replaced by a technician called Margaret. The most diverse and important of them is Galaxy News Radio.
Fallout 3 contains several in-game radio stations.
