There's a wiki article on the subject of nurses who kill their patients. It contains some general speculation on motivations.
The motivation for this type of criminal behaviour is variable, but generally falls into one or more types or patterns:[4]
Mercy killer: Believe the victims are suffering or beyond help, though this belief may be delusional.
Sadistic: Use their position as a way of exerting power and control over helpless victims.
Malignant hero: A pattern wherein the subject endangers the victim's life in some way and then proceeds to "save" them. Some feign attempting resuscitation, all the while knowing their victim is already dead and beyond help, but hope to be seen as selflessly making an effort.
None of them seem to fit here. A mercy killer would only work if she views the world as so bad that she spares the babies the suffering in growing up inside of it, but she seems to acknowledge that she's a terrible person. This fact also makes me want to cross out the sadistic one, because I feel a sadistic sociopath wouldn't end up feeling remorse. And from what I can tell she didn't try to be the hero either, not even sure you can with some of the ways she chose to kill them. Could maybe some sort of compulsion or deeper mental issues, like hearing voices or something. There's definitely something very wrong with her.
I don't know, all other actions seem very competent and very different from the note. Without thorough investigation by professional we can't draw conclusions from that. It may just be that she prefers people thinking that she is crazy rather than a heartless monster. The note seems very deliberately written to look crazy to me but who knows
That was my thought as well. Maybe she knew she was close to getting caught and hoped to be labeled criminally insane for some kind of imagined lighter sentence.
In the US, at least, being deemed insane by the courts lands you in unpleasant, secure psychiatric facilities whose patients are often forgotten and abused worse than inmates, but maybe it's better in the UK...?