He is sure to remember her dying face! (40)
Ugh, another kind of chilling death moment. This is where our speaker makes it clear that she doesn't have to kill her ex in order to get revenge on him. He will be tormented by the sight of his lover's dying face, and that should be punishment enough for him. Clearly, she's thought through every last moment of this death scene many times.
It kills her, and this prevents seeing it close: (42)
"Seeing it close" is a pretty good summary of this lady's whole attitude toward death. Most people try not to think about death at all, or at least they try to ignore the gory details. Our speaker, on the other hand, wants to look at it through a microscope. She wants to see every awful thing that happens. So, when it comes to examining the finished poison that's going to do the deed, she doesn't want anything to get in the way. She needs to get in there and see things up close, without the mask to prevent her from getting a good look at the seeds of death.