I think the real question is, who IS Rin and who wants to BE Rin.
Their identities are blurred. Rin's hair is textured more like Len's, and Rin normally wears hairclips on both sides, while here, they're both wearing a hairclip on just one side. Hence, they're both trying to be like each other.
That said, I kind of agree with Adpet-eX just looking at it - the one on the right seems to have a little more curves and has hair that sweeps more like Rin's normal part.