Mainly I've pictured Quina with a deepish kind of raspy voice, like Edwardo from Foster's Home, or Grover from Sesame Street.

Also, I think Quina has wondered what s/he is. Maybe all s/he needs to know is that s/he's a Qu and that's all the info s/he needs.

Or maybe s/he eats so much because s/he's long since given up hope to find another s/he to settle down with.

Or maybe Qu's have genders but Quina's an anomaly, or freak of nature, and has no discernable gender and that's why s/he was such an outcast in the Marshes.

Oooor maaaybeee Qu's have the power to determine their own sex and Quina doesn't know what s/he wants to be.