The term blue blood is a reference to nobility. The Spanish coined the phrase sangre azul which translates literally to blue blood. Grandmere Catherine is telling Ruby that her father comes from a very rich and elite family that would not want to tarnish its reputation for any reason.
The last words that Gabrielle says to her mother before she dies are ma belle mere. This translates to English as my beautiful mother. The relationship they had was obviously an important one, and this is another reference to the novel's prequel, Tarnished Gold.
Cajun music is essentially Acadian based zydeco. Cajun music is no longer confined to Louisiana. Country music has been influenced by Cajun music. Many Cajun songs are based on ballads and the lyrics are associated with a story.