How do I help my 14 year sister with her fear of Hitler?

My little sister is so scared to death of Hitler she can't even go outside. She is afraid Hitler will be outside even though we've tried to tell her that he's been dead a long time. It started when she had this dream about Hitler coming up through the plumbing and getting in the house so she makes us keep cement blocks on all the toilet lids and also on the washer and she will only take baths, no showers, so she can plug the hole. She says Hitler can come out of the sewer though and that's why she refuses to leave the house. I don't know what will happen when she goes back to school in August we may have to homeschool her. I don't even understand why she is afraid of Hitler in the first place since we are Japanese did she not learn any history?