My advice goes like this.  "I really believe in breastfeeding and usually
advise moms to breastfeed.  However, if you continue using drugs while
breastfeeding, your baby could become very sick or even die."  This mother is
going to do what she wants not only with regards to drugs, but also with
regards to breastfeeding and keeping her doctor's visits.  I would not
encourage her to breastfeed.  Bonnie