Head swaying often means they either have narrow vision or very poor eyesight, they do it to try picking up movement, if they sway from side to side they can pick things up a little easier. Get her eyes tested if you can, is she red eye'd? its most comment in them.there's not much to worry about I dont think. I have had a few rat who did that. They lived healthy normal lives appart from the swaying, i also had a REW rabbit who did it.