Even from the back the hair still looks slightly different to me.. that said it could have changed slightly while she was poofed. The gem shape is interested to me and makes me think of lapis, but taht said all the silloetts there use a simplified tear drop shape so it may just be stylistic there and not the true shap of the gem. Also her gem is larger and at the center of her back while this seems off to the side possiblyl, though I guess that could be the pose.
Also.. if the midle shade of blue was an aquamarien (though a taller one somehow) that would give us three gems that are actually all tear shaped. Maybe that's a common shape for gems in Blue Diamond's court. That would actually make sense.