The "you are going to kill me" was her state of mind at the begining. Purly based on instinct. Remeber henrietta also pointed this out about Grimms and Hexnebiest. You also have to remember she had the dream of hurting Rosalee. Until she actually killed the guy in tribunal it was only a dream. After Tribunal she realized should could actually kill if threatened. You have Juliette running on instinct doing things out of her nature. Why would she not think this would also be the case with Nick. If nothing else she would reason Nick could upset her and she could react. That is how she killed Rosalee in the dream. It was an involuntary reaction to an emotional state. The same as she experienced on Tribunal and when she blow up the car.
At the point where she did show Nick she had learned enough control to realize she would not kill by accident. That is why she said "would kill her" instead of "will kill her". past tense because that was no longer her concern.
Her new concern was would Nick accept her. That point she got it right. What hurts her the most, she would never think Nick would have as adverse reaction as he did. She expected shock but total rejection, that was more then she could take.
The thing that prevented any further discussion was when she woged and Nick walked out. His excuse was he needed some air. Not only would Juliette never have walked out. Juliette has never walked out on Nick and his problems. When Nick was a zombie in the barn. Did Juliette take one look and then walk out. It may not have been hexenbiest ugly, but zombie Nick is not a pretty sight. No she appoached him to give him the shot to cure him at great personal risk. Not once did she look at Nick other then it being Nick. See never once saw him as a zombie. Even afterwards when he was sleep and turned grey. She did not jump up worring that he might be becoming a zombie again. She went right to his rescue. She did not have to think about it. She did not have to go take a walk to clear her head.
Well it was a shock, Nick needed time to get use to it. Ok Juliette woges in the mirror. That is way more of a shock then seeing someone else woge. But Juliette instantly pulled herself together because her frined was in trouble and came to Rosalee's aid. Even with Juliette suffering her life changing change. She did not burden Rosalee who already was dealing with the idea that Monroe might be dead on her mind. So to say Nick needs time. I say Nick be more like Juliette and grow a pair.
The point where Juliette finally relized it is over, the dead manticore. For Nick to show no more concern then to say I am sorry. Showed her his lack of concern or a major case of denial. The kind of denial that would indicate Nick was not ready to be forcded to face the truth. Nick is a detective. Nick knows what a manticore is. This thing is dead on his floor, not with a gun shot. But with the same hole in his chest as in the other victims he has investigated. The is no rational or irrational explaination other than supernatural, and there are only two people in the room and one is dead.