Our president passed away and they have asked me to take her place. It will be impossible to fill her..

Normally, the president will have to promote you take their place. According to FAQ page: "After 30 days of inactivity (not logging into June’s Journey) the game will automatically transfer a President’s role to the most recently active Officer (or member in case the club doesn’t have other Officers). In this case, the previous President is demoted to Officer."

If you can't wait 30 days, you'll have to plan a way to start a new club and have everyone transfer over. This is best done if you have communication outside of the game, since you will lose all communication with teammates once you leave to start a new club. Or else you can decide the name of your new club, and let them know how to find it prior to your leaving and starting a new club.