All of my ruby and pink eyed rats sway their heads, especially if they want to jump/climb or if I move something in front of them. I wouldn't worry about it, it's how they gage distance and figure out their surroundings.
If she's a ruby eyed (black eyes with red tinge) or albino (red eyes), her vision won't be as strong as one with black eyes. It's normal for their heads to sway from side to side to be able to see better. My girl Aurora does this also