The art implies they were Robin and Supergirl before they became Huntress and Power Girl. This still takes place in Earth 2 and not the 52' Verse (well specifically the Earth 2 of the New 52 'multiverse) . Kara Zor-El is the Supergirl of the 52' Verse, and Karen Starr (so basically there are now two alternate versions of Karen) is a friend of Mr. Terrific.
As for the design, this is the best of the bunch in my opinion. Really is an alternate reflection of Kara's current costume design.