Unlikely, given how unnatural it was for any Goblin to take adventuring class levels, according to anyone but Fox and the Party. (I'm assuming that Young and Beautiful was an Adept, and that NPC classes are part of Goblin tradition.) But a Thuntemplate is always possible; Duv might actually be God-Blooded or have a Maglubiet variant of Lolth-touched. Half-Fiend seems unlikely though, since that would probably give her demonic bat wings instead of angel-style white feathered wings. Perhaps she's Half-Celestial as I suspected, with the alignment details waived for Rule of Cool.
1/2 celestial requires being born good, you can become evil later and keep the template.