In a dark timeline where the war with Robotnik is not simply a bunch of kids fighting an idiot genius, but all out insurgency against a dictator planning to subvert life and free will at any cost.
Amy Rose isn't the same fangirl perky teenager chasing the blue blur, but a soldier, hardened and scarred by the war. She may have lost an arm, but she's still got one left, and thats one more then she needs to kick some machine ass.