Never heard of her before, can someone explain the significance? I see that Autobiography of Red is praised for blending different things like translation/novel in verse/essays together, but that doesn't sound like something new? I've read Milorad Pavic's Dictionary of Khazars before, seems like it fits the same description?
Among other things, Carson is a famous/prolific translator of Ancient Greek plays (including the ones that probably come to mind when you hear "Ancient Greek plays").
Why assume that novelty is a criterion for the worth of someone's literary output? Things can tread familiar ground, use familiar forms, and still be remarkable or worthwhile. (Imagine saying to Shakespeare: "Why write a book of love sonnets? Didn't Petrarch already do that?")
That said, I haven't read more than a few pieces by Carson and I'm curious to read more.
She is typically praised for her translations as well as the creative interplay of classical and modern imagery in her works. An aspect I think often overlooked is the relation of her text with the physical media of reading the text. For example Nox which is printed as a single continuous accordion-folded sheet.