Wouldn't it be ironic if childhood malnourishment made her infertile? Or maybe she takes after her dark elvish ancestor in ways beyond her eyes, what if she simply hasn't hit puberty yet (which would also explain her small bosom), and is primed to blossom on a more elvish schedule rather than human? That would perhaps imply that one of her parents was a secret half-elf. Better hope she never gets her DNA tested!
Given that you're planning to add pregging eventually, Runey, I didn't really think she'd be outright infertile, this was spaghetti-at-the-wall speculation, but it would be ironic. An interesting twist. Maybe consider it an alternative ending. Were it the case, she could still get her wish of "having" a dozen kids by raising all of the babies Our Hero is going to be making with the rest of the harem! One kid each from Lin, Kali, Lucia, Maria, Hana, Felicia, Emma, Autumn, and Ellen gets us most of the way there. With options for Moon, Kate, Juliet, Jin, the Sanctuary elves, and the two Queens, that puts us over a dozen. Then throw in the college girls like Vanessa and Nidra. And yes, I know how old Ashley is, but what age do elves hit puberty in this world? Given how long-lived they are, their puberty could QUITE REASONABLY come later in life than humans... and could be a contributing (though not primary) factor in their in-game population decline.