I was never talking about the time when Juliette became a hexenbiest, but the years prior to that. I think she saw the writing on the wall when Nick lost his grimm. If Nick was unhappy enough to confess to Monroe that he wanted his grimm back, it seems to me Juliette would have seen his unhappiness as well. Perhaps she figured at that point, she was never going to be able to compete with his life as grimm.
The best way to frustrate a cyberbully is to ignore him.