Her cache is a letterbox hybrid so the posted coordinates are just a starting point for finding the container. Walk like a penguin until you are standing under the centre of the arch. Face west and do the Penguin Shuffle one metre toward the lake (it's on your right). Now take three penguin-sized steps backwards and peer over the edge.
If you have followed the instructions correctly, you should find yourself standing directly above the hiding spot.
Along with the log, pencil, and swag for trading, inside the container you will find the usual letterboxing kit so please stamp your book. When you have finished, please make sure the cache in well hidden.