Dear Ms.Maitreyi Haldar,
This is with reference to my previous query (query no.​8920821): Who does William...
Well, the link provided by you does not answer my query for it is giving an introduction/analysis for the poem.
It is not telling who "she" is in the poem.
Please, just give the name of the person "she".
Who is "she"???

I apologise for my error.
This poem is the only poem in Wordsworth's "Lucy" series that doesn't address her directly. Therefore the identity of "she" is speculative and vague. There are many theories related to the identity of "she", but the widely accepted theory is of her being Lucy. 
Lucy is almost a mythical character that has been conjured in the poet's sub conscious, and therefore he "slumbers" since he is aware that Lucy isn't real and is a figment of his imagination.
This is a complex poem which requires a deep understanding of various literary devices and a thorough knowledge of the background. As per your Grade, this poem has been simplified in your introduction and that is why I sent you that link.
I know that this explanation too might be difficult to understand, but I have tried to present a complex matter in a most uncomplicated manner possible.
If you feel that you need further explanations, do revert back and i will do all i can to help you. I'm happy to see you exhibit such curiosity for literature. This is a very good habit and it will help you understand literature better.

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