I read it in the 1970s. It was written for girls, maybe came in two volumes, the copies at the library had stripes on the covers. Came from the Beverly Hills Public Library, if that is helpful.
I think it took place in a girls’ boarding school. Maybe there was one girl called Cordelia, shortened to Cordy. Maybe in it they told a story about a Castle Drachenfels. It’s possible I’m mixing this up with another book, but maybe not.
Please help! Thanks!