Who is Maria Ellen Hornblower ne Mason from Hornblower and the Hotspur and what is their importance?

Maria Ellen Hornblower is Horatio's first wife. The two meet when Horatio takes a room in Maria's mother's home. Maria is described as a consciencious wife, who takes care of of her husband's needs, unfortunately, Horatio sees her efforts as clinging and irritating. The couple has two children, both of whom contract smallpox and die in childhood.