Nick tells Juliette they will "figure this out" in regards to her having become a hexenbiest, to which Juliette tells him it's permanent and there's nothing they can do about it. Nick should have realized right away how to cure her of this affliction because of the time he took away Adalind's powers. Even if for some reason it wouldn't work the same way on Juliette, Nick should have thought to suggest trying it right away.