It's just my opinion but I suspect her motivations for alerting the nurse are a little more nuanced, if she's guilty.
I think LL's actions, if she's guilty, showed consciousness of situations that could escalate and backfire on her, by for instance not reporting two monitors that hadn't alarmed, texting about babies looking sick when she took over, asking who was talking about her babies, establishing a narrative amongst her friends of being bullied which might in reality have been staff questioning highly unusual collapses on her shifts, changing methods and establishing consistency of 'problems' with certain babies, putting false information in the notes etc. If LL walked away as soon as the nurse returned, baby I might have died before nurse discovered there was a problem - leaving open the hole that baby had collapsed while LL was watching her. I think LL, if guilty, had to tightly control the emergence of the problem as happening now, in front of nurse, not before.
JMO