Though given Elves soul-bond at marriage it'd be cruel to tell her she wasn't married to Thranduil without further intervention, in my opinion.

We know Thranduil had a wife. If this is her, she'll just wind up wherever Thranduil's wife is supposed to be, afterwards, once you get canon to snap back.

The cool thing about canon snapping back is that it can fix pesky little things like false genetics. Neuralyze her, tell her she's no relation to the royal family, and let canon take its course. QED. {= )

~Neshomeh, who's doing something similar in her current mission, hopefully to be released very soon.

neuralyse and let her assimilate into the canon. Thranduil's wife isn't mentioned in the books, which is why those who've read them tend to assume she's either dead or left for Valinor. As far as I know, neither is true; she just wasn't mentioned because she wasn't of any use to the plot.

The mission you read was actually one I co-wrote with Kgarrett; we decided to recruit the brothers of Legolas (and the eldest's wife and kids) because they were shoehorned in to facilitate Legolas's whiny bratty teenager-ness. Legolas was never mentioned as having brothers, and we decided it was seriously improbable for Thranduil to send his youngest son on a dangerous quest, and also for him to have children over a millennium apart in age. Also, the brothers' basic personalities were not very consistent with typical Elvish behaviour, particularly royals, so we recruited the lot rather than have unexplained extra kids of Thranduil running around.

If Thranduil's wife is basically inoffensive to canon, you can likely get away with neuralysing her; after all, Thranduil had to be married at some point, or there wouldn't be a Legolas.