Shelby tells me about her bathtime visitor

I was working on my computer downstairs in the unfinished basement yesterday evening when Shelby came downstairs after her bath to tell me about a visitor she just had.

She claims that a white shape kept darting in and out of the bathroom doorway . She kept seeing it out of the corner of her eye, but every time she tried to look at the doorway nothing was there. This happened she said for a about a minute, then stopped.