More info about the name "Merletta"
Merletta is a diminutive of Merle. Merle is a variant of Muriel. Muriel is probably derived from Gaelic elements, which ultimately mean "shiny sea". It was popularized by Dinah Craik in her novel John Halifax, Gentleman, where Muriel is John Halifax's daughter. The name itself was not popular outside of Scotland until the beginning of the 20th century.