The answer is there already... But I guess that she doesnt have any powers plays a role in it too. I have one question. Why do you hate Amy so much? I know she is a little naive, but hey! she is just a little girl. She'll grow up and change.
It's actually because she's compyright to the Archie comics, if i recall correctly. Hence why the other freedom fighters (Bunnie, Rotor, Antoine, etc) and Scourge and his Supression Squad...characters like that arent in games either. I could be wrong, but im pretty sure that's the reason. Sega didnt create her, Archie did.