Woman is not a terrorist. In all likelihood she is schizophrenic. A classic symptom of schizophrenia is hearing voices in your head, and sometimes even having imaginary people be a part of your life. For an idea of what this is like, I'd suggest seeing the Russell Crowe movie "A Beautiful Mind". For some people, the voices in their head is described as "aliens speaking to me". For someone with a somewhat misguided religious fervor, the voice of shizophrenia in their head is often described as "God speaking to me". Whether its God or Aliens that schizophrenics believe are speaking to them, it's a tragic but not unheard of occurrence for the "voice" to tell them to kill people. If the woman in this case is schizophrenic, she should be confined. But I believe the confinement should be in a mental health facility. This will probably start a whole new debate, so I'll stop that train of thought.
But to answer your questions more directly:
1) She's not a terrorist. More likely she's a schizophrenic. For terrorists, it is not actually god who tells them to kill people. It is a charismatic, manipulative leader who has decided to use religious faith as a means of political/mind control to coerce others into acts of violence in order to achieve the leaders own personal agenda. Yes, Osama Bin Laden is a clasic example of this.
2) As my initial answer says, it can be aliens who tell an insane atheist to do it. Could also be anything from imaginary friends, huge mega-corporations (i.e. Microsoft), or the government that "tells" people to do it. There is a wide variety of ways that schizophrenics have described the "voices" in their head.