How can we convince my niece Santa will come?

My sister moved to a new house, because she was burgerlized .This new house doesn't have a chimney...yeah, so thats the problem...we have told her, we will open the door, or he'll come through the window. She is scared of someone coming in through the window to rob them. She doesn't trust anyone answering the door late at night, so she is panic. She is 8 yrs. So the whole story of santa not being real, is yet a ways off. Wha can we do to asure her...he will come.