While discussing bodily functions is generally inappropriate, I can see some instances where she may have felt the need to tell you why she was using the bathroom. Perhaps she thinks you perceive her as lazy, as uses bathroom breaks as an excuse to get away from work. Or perhaps she feels you like information on what employees are doing. Either way, I just feel there may be another issue here to be mindful of. That doesn't excuse the comment, and you did the right thing. Still, there may be a few layers.