Ivy comes back later that night as she knows Zack will do the interrogation himself against Officer Dan and also the doctor. She didn't have too, but she feels the need to see that herself in case Zack is losing himself.
She stood there while lean her back to the wall. At that time she realized that the doctor was already gone and only Officer Dan was there. She made her own conclusion at the time that Zack probably wanted to deal with Officer Dan first before the others or he has already done with the doctor. But as long as there's no one die there then its fine.
Seeing Zack face there Ivy knows that he must be feeling betrayed so much inside his heart and hurt as his own colleague is the one that stabbing him at the back. No matter what the reason is. Even if Officer Dan is not the one who kill Rosa, he is still indirectly killing her by covering for Bennet. And Ivy can't seem to find a reason to forgive him, and Zack probably thinking the same.
