Its the evolution of the Grimm world. Juliette had her place at beginning. No TV show that had the same couple from beginning to end. This was always the end game of Grimm where Nick ends up with Adalind. That's the awesomeness of the story is that they were once enemies/nemesis and now they've evolved. Now that Eve is human, she has no place in the Wesen world. She can't protect Kelly from possible harm from other powerful Wesen.
Plus I have a feeling that Juliette/Eve will die anyways.