Worldwired - Elizabeth Bear

As long as there's an Earth to defend, Jenny Casey has a job. But she may outlast the world she was custom-built to save. . . .

Give Canada's Master Warrant Officer Jenny Casey an inch and she'll take a galaxy. That's just the kind of person a world on the brink of destruction needs. The year is 2063, and Earth has been brutalized. An asteroid flung at Toronto by the PanChinese government has killed tens of millions and left the equivalent of a nuclear explosion in its wake. Humanity must find another option. . . .

Perched above the devastation in the starship Montreal, Jenny is still in the thick of the fray. Plugged into the worldwire, connected to a brilliant AI, her mind can be everywhere and anywhere at once. But it's focused on the mysterious alien beings right outside her ship. Are they there to help—or destroy? With Earth a breeding ground for treason and betrayal as governments struggle to assign blame, Jenny holds the fate of humankind in her artificially reconstructed hand. . . .