Animating a static image

I started with the " Walk animation " hands on tutorial. i modified it a bit . Works as expected. Added a motion tween to the Background as explained in the tutorial. It all works as expected. So far so good. I then added a static image,  School_girl_side  ( as can be seen in the attached image) . Linked the static image to the background. It appears like the boy is walking towards the girl. Still working as expected . At this stage, i wanted to animate the School girl frame by frame while the rest remained the same. So on the School_girl_side "layer" , i did the "Convert to frame by frame Animation" and selected the option " Keyframe every fourth frame" . at this point if i move the girl to a new position in a particular frame, she remains in the original postion in the other frames, but at the new position in that particular frame where i moved her. But if i move/alter parts of her , her eyes or mouth in one single frame, the changes get applied to all frames. i also tried the options " break apart" / "distribute to layers" , but i still can't change individual portions of the girl to be different in multiple frames . How can i accomplish this ?  Thank you.