Alan Dean Foster expanded M'ress a bit in his adaptations of TAS episodes.
Thanks; I meant to post that as well, but I got distracted while composing and forgot. I'm not sure if his material influenced the Lincoln Enterprises "bio", or if he used the "bio" to frame his background "anecdotes".
But the base theory still holds. From "on screen" evidence alone, M'Ress could be, in theory, any number of things.
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Kirk: "So, Lt., any native holidays of which I should be aware?"
M'Ress: "Huh? uh, Captain, I'm from Earth."
Kirk: "But your appearance...I thought you were another species."
M'Ress: "Oh, this? Nah, I'm just a big fan of 'The Lion King'."
Kirk (thinking): "How the %^&* did she pass the 'Fleet psyche exam??!!!"