I'm sure the mother will have had mental health assessments, and if the defence had been making a case for leniency based on mental health issues it would have been reported.
This woman raised other children, ran a home and held down a job. She would have had a midwife health visitor etc. with her previous pregnancies and known how to access them, could have called her GP, asked her parents for support even spoken to someone at work or one of her DCs teachers.
I agree she probably made some poor decisions during the pregnancy but it was her decision to compound that by not seeking help once the baby was born.
Her other DC, of young, would most likely have accepted not going in her room and the tv or radio playing as normal.
The boyfriend was certainly presented with red flags, but possibly was being respectful to the dc by keeping out of their space, who knows, I suspect he was curious and took an opportunity to investigate at which point he seems to have done the right thing immediately.