The issue was never addressed in the show.
Interesting question, to say the least. I dn't think it would be wise to have an EarthGove rep (or a Minbari rep). It would just piss all the other races off. "Two humans!!! If they get two, we get two!"
Besides, Sheridan is sorta an Earth rep. He's a member of Earth, although I wouldn't say he represented Earthgov. We just never got to see any major situations concerning Earthgov in season 5. The only think I can think of is when Sherdian talks to Delenn about a joint Earth/Minbari ship building project. Sheridan said he had talked to the Earthgov President. Perhaps that means he does represent Earth.
And Lochley was not a rep, she was simply captain of B5. There was even a line, where Sheridan said somethin like, "If it concerns the Alliance it's my territory, anything else is yours."
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We're all born as molecules in the hearts of a billion stars, molecules that do not understand politics, policies and differences. In a billion years we, foolish molecules forget who we are and where we came from. Desperate acts of ego. We give ourselves names, fight over lines on maps. And pretend our light is better than everyone else's. The flame reminds us of the piece of those stars that live inside us. A spark that tells us: you should know better. The flame also reminds us that life is precious, as each flame is unique. When it goes out, it's gone forever. And there will never be another quite like it