I know this isn’t going to be a popular opinion, but I don’t think she murdered because had this uncontrollable urge to harm innocent tiny babies. For me, I think it was more a means to an end for her.
She enjoyed the attention it gave her. For the first time in her life (we heard she wasn’t popular at school, doesn’t seem to have had much male attention etc) she was the centre of attention. from her colleagues, (you’re having such a bad run, are you okay? How are you?) from dr choc (poor lucy, here’s some chocolate for you) and she probably found it exciting and even thrilling. It gave her something to talk about all the time. she texted about it non stop. Even to her mum (just lost another one overnight, it’s so sad) almost like she was baiting for people to sympathise with her, tell her how strong she was, how good of a nurse she was. And they did exactly that!