I have read that several times on MN over the last couple of days, with at times added comments blaming the pressure to breast feed that is put on new mothers. But surely if a medication is unsuitable when you are breastfeeding then it is unsuitable during pregnancy too?
I think, as with most medical things, it is a balancing act. Medication might not be ideal during pregnancy but if the benefits outweigh any damage to mum and child then it is better to continue.
Once baby is born it is a different balance, in a totally different context in the UK an HIV+ mother is not encouraged to breast feed. The transmission of HIV to the baby can be prevented during pregnancy and birth and then formula feeding will continue that.
In a remote area of sub Saharan Africa an HIV+ mother will breastfeed because it is the best option for her child as formula is difficult to get, may be made up with contaminated water, may be given dilute to make it last etc etc
As for the question of murder - this woman was ill, her illness caused her death and probably hat of her child. That is the same way as (sorry using Africa again) a mother with ebola may pass the disease on to her child and cause the child's death.
Mental health issues are exactly the same as physical health issues in that some are acute, some chronic, some are deadly, others mild, some can be passed on genetically some are caused by the environment.