This poem was written in free verse; it has no set rhyme scheme or meter. One interesting thing about the poem's form is that, in a way, it shrinks as it goes along.
The poem is made up of five stanzas. The first two are quite long, but they get progressively shorter. The stanzas become short once Elizabeth asks her big questions. Since Elizabeth is never able to answer the questions, the poem falls apart into those last two very small stanzas. It's almost like the gaps between the stanzas reflect her inability to answer the big questions that she poses. Instead of answers, we get (almost) silence. So, even though the poem is free verse, its form still affects its meaning.