The nautical stuff is just from her being Verdemarian and living by the sea. The jazz stuff is likely connected to Cordelia, because Ermelinda doesn't have jazz as one of her musical interests.
My headcanon is that she's descended from one of the pirate exes of the original Cordelia. She may have developed a fascination with the Thebe lore beyond just being power-hungry, so her son marrying into the family had multiple bonuses for her. Maybe she even played up her fascination to ingratiate herself with the Thebe family. It was only later that she realized that she couldn't control Cordelia V, - and that Cordelia V in general had bad vibes- which is why Ermelinda hates her.
