In my headcannon, those two bond as siblings. Playing. Fighting side by side. Supporting each other. Joking. Singing.
It be sweet to see the human one bond with her pony twin. Many humans see ponies as mindless. But this one sees an equal. It be awesome and heartwarming to see her cheer on her twin, risk her own life to help her, and cry for her. For examole, she gets upset when jerks shoot her and fights to protect her until she is healed, and her pony twin saves her in return…… A big example of their sibling love. And also, the human one scolds Twylight for the Marer Do Well and Walking Dead hoaxes, the division between Rainbow and Rarity involving the swamp, the cheerleading incident, and more wrongs on her pony twin; protecting her spiritual sibling.

They earn it well.