To hide her "mortification" under it
Where is your evidence? So I can answer the question
If you had shared the options It would have been much easier for me to answer in suitable form for you. But actually I have got the answer and do hope it could help you. I am more than sure that the repetition of "nevermore" creates a unity of effect on longing. The only word that Rave knows and uses all the time to respond is "nevermore" so that it gives a circular sense to the poem.