Well, not exactly sure how detecting youkai works, but going along the myth in which gumihos become 'human' if they abstain from eating humans for 1000 days or something, and considering Toshiko won't even let the kids see a corpse or touch a gun, I doubt she'll inform him that one of the detectives is a cannibalistic youkai. And Mearii's pretty good at keeping quiet.

The worst scenario would just be that Jun would think that she was an illegal immigrant working as a youkai hunter (maybe to escape loan sharks from some foreign gang), I'd think. XD