for me it was when Michael went to confide in her about how Denise was making him feel and asked for her ehlp in getting her to back off him.
She said all the right things to him and listened intently and tutted in the right places and told him she'd do her best.
Then she went and gathered an audience and slagged him off and wound Denise(her best friend)up even more.
And then went on her saintly way.
See, I thought she dealt with it quite well. She made sure Denise didn't go and try to talk it out with Michael, as he was feeling 'unreasonable' towards her, which he was, at the time. She did try to be diplomatic about it all, which is seen by some as being two-faced, but as things got worse, she was prepared to tell him the honest truth.
I'd have to watch it again to make any further comment, because my impression isn't the same as yours.
I quite liked Natalie at first but that episode turned me right off her, she then went on to compound it with her own arrogance, which was probs just her being honest too...