I thought it might be funny to have Yun ask Vesta what was wrong with her sister... but I don't think they look anything alike, so that'd be a bit far fetched for a mistake.
Actually, the only description of Vesta we've been given is that she's "a beautiful young woman", while we know that Maridosen is dark haired and pale skinned, which of course means she must be evil. So I suppose it's possible that they're related.