Women who kill their babies are often unknowingly suffering from postpartum psychosis. :(
I actually thought my daughter was suffering from it just after she'd given birth (nearly a year ago now!). She stayed with me for a week after the birth and one night she woke me shouting that the fire alarm was going off. It wasn't, so I suggested she'd fallen asleep feeding her baby daughter and dreamt it. She insisted she hadn't fallen asleep and that the fire alarm had sounded, so I went to look for the source of the smoke (even though I couldn't smell anything). There was nothing amiss but she absolutely kept insisting it wasn't a dream.
Knowing about postpartum psychosis, I began to seriously fear she'd hallucinated the whole thing and felt very worried. Luckily, nothing similar happened and we both agree now she fell asleep momentarily and dreamt the whole thing. Phew! :)
I hope nothing bad happens to Stacey or her baby. :(