a couple of points stand out to me:
whatever West African practice may be she must have been doing something different: there is a large W.A. community in this country, yet deaths like this are not common occurrence
she had been educated: health workers had been pulling her up on this practice before and she had refused to listen- so she could hardly plead ignorance
she is supposed to be a trained nurse, yet she believed there are no nutriments in milk
conclusion: there is something wrong with this woman that you probably couldn't solve with an educational class in infant nutrition
but I could sort of see how cultural practice might get the husband off: if he is West African too, he probably would never have learnt anything about infant rearing and may well have been expected to keep out of it
and if he is not a nurse and has not been involved with health practitioners, he could arguably plead ignorance