The only Sebastiana Mendez I find is Sebastiana Méndez Pereira (-1875), sister of Joaquín and Adolfo Méndez Pereira. She married José de la Cruz de León Caballero (1830-1910) on 11 July 1857. Sebastiana, Joaquín and Adolfo were children of Joaquín Méndez Pourez, original from San José Costa Rica, son of Joaquín Méndez and María Pourez. Pourez could be a typing mistake. It could be Pérez. But it could also be a foreign last name so I leave it like that.