My character already is in the animated ID array. And I am almost 100 % sure step anime is actually set to true while defending. What I think is happening is that when defending, it updates whether you are or not each frame. Perhaps something like @sframes is being reset each time, so that it's always on the first frame? I'll try playing around with it...
EDIT: YAY! I got it. I had to edit setup_sprites so that it would only setup the defense sprites once, then sprite_update so that it would change frames while defending. Well, I kind of got it. The sprite animates now, but it's not the right sprite... But with a little more tinkering, I finally got it! yay! animates the defense sprite!