I agree, there's unsourced criticism here: 

 'Geraldine, who initially appears to be an almost mirror image of Christabel, is later revealed as being far more complex, both sexually and morally:' 

 and then the quote given is mysteriously missing it's second half (something like 'behold her bosom and half her side, a sight to dream of, not to tell, oh shield her, shield sweet Christabel') I always thought that far from erotic, that stanza was meant to be horrific - i.e. Geraldine unclothed has some sort of marking or grotesquerie (as a child I imagined she was a rotting corpse on one side when I read this) to further distinguish her as supernatural evil.