If Link tries to talk to Elsie at normal size, she will not speak coherently and instead will just scream out cow noises. Link is able to speak with Elsie while in Minish form. To do so, Link will first need to acquire the Pegasus Boots from the Shoe Shop in Hyrule Town. Once he has these, Link can return to Lon Lon Ranch and, just north of the house, there is a tree that Link can dash into. This will reveal a Tree Stump that allows Link to shrink down in size. From here, he can enter the right side of the house and speak with Elsie. Elsie has a fear of one day turning into ground chuck.
Link is able to fuse Green Kinstones at various points in the game with Elsie. As it is a Green Kinstone fusion, it is not set to a specific treasure chest, but instead, one of the many possible treasure chests. There is one random Red Kinstone within the game that opens up a location in the Hyrule Castle Garden leading to a Piece of Heart, as well as a random Blue Kinstone that opens up a tree in North Hyrule Field leading to a Fairy Fountain. Elsie is one of the many characters in which Link can make this Kinstone fusion with.