Small tanks barely use any electricity at all. Tell her you'll be more careful about turning the lights off when you leave a room and that will more than offset the electricity used by a small tank! The lights aren't on 24/7 (and use very little when they do), the heater only kicks on when it's too chilly (and is also a very low power draw), and filters are VERY energy efficient. Tell her to register for this site and we'll talk her into it lol.