Does a recurrent metaphor structure the poem?

One interpretation might be that there isn't a recurrent metaphor in this poem. There is some figurative language—Dickinson uses a simile to describe the atmosphere in the room where she is dying as "like the stillness in the air—before the heaves of a storm." But, by and large, with the exception of the "King" Dickinson expects to see (who may be God or perhaps death himself), what is described in this poem is described literally.
What certainly does guide the structure of this poem is the motif of the fly, which is introduced in the first line and then serves to change the funereal tone of the poem quite abruptly when it "interposed" at the end of the second-to-last stanza. Now, there is no suggestion that this is anything other than a literal fly. The fly is supposed to be something unfittingly mundane, distracting from the somber atmosphere. At the end of the poem, it works itself "Between the light—and me," which may suggest that it fills the dying woman's vision, or even that she sees it against the backdrop of the metaphorical "light" into which the dead go. The fly certainly governs how we approach this poem, but it is not necessarily a recurrent metaphor.