Did you read the article? The amount she was taking would not normally have caused any problem - in fact morphine/codeine are less harmful to a BF baby than other painkillers.
"Trace amounts of painkiller appear in the milk of women taking codeine or morphine, and a fraction (roughly 10%) ends up in the child – 2 or 3 billionths of a gram – the effects of which are negligible. No morphine-related death from breastfeeding has ever been reported in a peer-reviewed journal"
and
"Either a massive dose, 50-100 tablets of the type of morphine prescribed for the mother, was administered orally to the baby, or a genetic defect prevented the baby from metabolising the tiny amounts of morphine transmitted by breast milk."
It is an awful story, not because the poor woman was taking meds while breastfeeding, but because either she or the baby had a genetic defect that messed up metabolism. Around 60 % of SIDS cases are due to a genetic disorder - this case is more like that.