^^^ When she initially became a hexenbiest, before it corrupted her, she started being an extremely useful member of the team. She was really coming to her own and her confidence was building. There was a short stretch at the beginning of the season where I personally felt her character had really gotten good and things were clicking. Then the stuff with Adelind started happening and Juliette went downhill fast. Don't get me wrong, I'm not defending the general quality of the character - Juliette was always my least favorite character of all of them but I do think that she did have a handful of good eps and that was about it.
But you're right, before amnesia she was completely worthless IMO.
I don't tink she was completely worthless, it's just that teh amnesia storyline was her first real storyline. And I think she kind of liked becoming an evil hexenbiest, but then I think many actors like playing evil parts.