According to Memory Beta, Caithlin Dar was half-human/ half-Romulan. It actually says her dad was from Ireland, and mother was Romulan. I don't know where the asian features are supposed to come from. Maybe when the Irish mate with Romulans, you get asian looking Romulans? I assume this comes from the novelization of STV.
That begs the question, though: how can she be half human when humans didn't even know what Romulans looked like 19 years earlier?
EDIT: I looked her up, and it seems she is just one quarter human, which makes it even stranger.