Complex sentence: She sees a shadow out in the hall and hides in her closet, thinking it's Fenton, but she learns the shadow is only Winn and Fenton grabs Donna in the closet.
Split into simpler sentences: She sees a shadow out in the hall and hides in her closet, thinking it is Fenton. She learns the shadow is only Winn, and Fenton grabs Donna in the closet.