IIRC Deanna had a key to the house and when she let herself in she smelled cookies baking and saw Jodi Arias sitting on the couch using Travis's laptop.
Personally, I'd really like to know when this happened and what else transpired. Deanna lived about an hour away at the time and had agreed to check on Napolean while Travis was out of town. She never saw a car parked in the driveway or on the street.
Why did she need a key? The doors were always open and the besties had the garage code, too, right