With the power still out, it would have been virtually impossible for Trina to have printed the photographs from the pool party that she is later shown, by candlelight, hanging to dry. While she could conceivably have used some non-electric light source, she would need to be very skilled at doing so and that is something that no one who is used to working with an electric enlarger would know how to do effectively.
When Roger gets home, Janet has the fridge door hanging open. Someone as fastidious as she would know to keep it shut during a power outage. Even though the power has been off all day, the frozen food would still be safe with the freezer unit kept closed.