Wow, so I'm not the only mother of an autistic son who thinks of such things? Wow. You're the first person I remember encountering who understands this.
The frustration factor was my first thought, too. I can even understand her comment about feeling nothing (being in shock at what a terrible thing she just did) and wanting normal children -- if her culture/family doesn't accept and support special children it's especially difficult.
I live in fear of what my son is capable of- he has hurt his sisters, tried to hurt me, and threatened our whole family. I have told health professionals this, and they pretty much just shrug and tell me there is nothing that can be done. I am afraid that he will do something that will become a criminal matter someday.