There could be many reasons. If she is older, she may be expressing pain as she walks. If she is unfixed, she may be trying to tell you she wants out to mate. If she was abused at some time prior to your arrival, she may be thinking she is back there there when you walk around. If she is just an original of her own, she may be smelling something that was brought into the house when you walked around outside. Even if we can't smell it, the other cats can. I suggest you play with her when you have to walk around to keep her busy. If she is occupied while you walk around her, she may be too warn out to respond to the stimuli. Get your mate involved so the cat learns positive things from him as well.