Such a complicated case.
I do wonder if it was a case of a bit of knowledge is a dangerous thing. She was trained in edge of life stuff, how tiny amounts of the wrong drug could have a catastrophic effect. And I wonder of one day she tested that theory. And the adrenaline and sympathy she got as well as the lack of suspicion made her bolder and made her crave that attention. Until eventually she was an out and out killer. That with that first death came the chance to place her self at the centre of a tragedy, receive cards telling her how wonderful she was, how grateful the parents were. Then she got to bathe the babies, dress them, take photos and hand prints. Become instrumental in a family's journey.
The she also discovered that the doctor seemed to be flirting with her. What better way to get to see him than getting him paged to the emergency and then working together: he obviously thought she was a good nurse. Perhaps she performed well in these circumstances and that 'praise' was warranted. But she had to engineer these situations, and so she did.
What she didn't do, was think about the actual lives she was taking or the lives she was damaging. It was all about her. What she wanted, what she needed, what she got out of it.
I also wonder if she thought (in the way narcissistic people do) that she was cleverer than everyone else. There was a suggestion that one of the reasons she talked to the police was to see what evidence they had on her, because she thought she'd been so clever that they had nothing. And in some senses she was right. There was no DNA, like there could be in other murder cases. Very little forensic evidence. Lots of circumstantial evidence, but of course there would be! She was there, everyone knew that. She worked on the babies, trying to save their lives. Full on hiding in plain sight.
The notes suggest she eventually became conflicted about what she was doing. Like a drug addict that doesn't want to be a drug addict, swears to themselves they won't have the next hit, that they hate themselves for being so weak, that they will beat the addiction with willpower. But of course they don't. And then the cycle starts over. It would be akin to a drug addict working in a pharmacy. Every time you go to work you have multiple opportunities to take those drugs, and you need that hit, and you take that drug. And it works. You feel better, until it all wears off and you realise again that you're weak. And you hate yourself for it. Eventually you lie to yourself. Convince yourself of an alternate truth. Convince yourself that these babies would have died anyway. Some absurd internal struggle. Again, all about her. And I'd bet she's convinced herself that she's innocent. Helped by the fact the hospital management acted the way they did, making the doctors apologise to her.
And even now, it's all about her.