Louise and Emma's Locket first appeared in the episode "Shipwrecked".
Emma met Louise Chatham at the pier where she was having an argument with Zane. Upon finding out that she's getting evicted from the pier, Ms. Chatham had a heart attack. Zane overheard her telling Emma about her "treasure". Emma later found the locket from the Lorelei shipwreck, as Zane was searching for it because he thought that it was a big treasure (he threw it down because he was disappointed that it was just a small piece of jewelry). Miss Chatham was very grateful when Emma gave her back her locket after her boat sank, and she told Cleo and Emma about her friends Gracie and Julia.
Emma's locket originally belonged to Louise Chatham who was a mermaid over 50 years ago; Louise's locket has a white stone - possibly a diamond. This could probably symbolize the water's freezing ability. Louise is the the only former mermaid still alive, as both her friends Julia and Gracie have died.In the episode "In Too Deep" Louise gave her locket to Emma, claiming that it felt right when all three lockets of the former mermaids should belong together with the new generation.