Jasmine is a character that appears within The Minish Cap. She doesn't appear into later in the game after Link has completed the Royal Crypt. At this point she can be found sitting just outside of Mama's Cafe, drinking a bottle of milk. When Link talks to Jasmine, she even references that she hasn't been around and that she praises Link for being attentive. As a reward, Jasmine will give Link a Red Kinstone.
Link is able to fuse Green Kinstones at various points in the game with Jasmine. 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. Jasmine is one of the many characters in which Link can make these Kinstone fusions with.