It's not really made clear in the adaptation until later, but Celia Ryder is the sister of Boy Mulcaster (Jeremy Sinden). So when it seems she is saying of Julia Mottram that she was "a girlfriend of boys" she's actually saying that she was "a girlfriend of Boy's".
During the storm, the first song the ship's band is playing is "Isn't This A Lovely Day?", written by Irving Berlin for Top Hat (1935).