Jan: It's not up to me to determine when BF is best or not. That's a decision that should be left entirely to the mom and partner, with the advice of mom's medical practitioner of choice.
Typical "no-no" situations would exist if mom was a drug/alcohol abuser, HIV positive, taking chemo/radiation, taking Lithium or other drugs that can build to toxic levels in the child.
Mom might also rethink the issue if her health could be impacted in any way: say mom was severely malnourished, had some long-term debilitating illness (I know several mothers with Rheumatoid Arthritis and MS and other illnesses/diseases/conditions that chose not to BF because it was very taxing to them), or had to choose between taking medication to treat an illness/disease/condition and being able to adequately care for their child or not taking the medication and having problems that could impact their ability to care for the child.
Providing information and support and helping moms weigh options is what lactation consultants, in my book, should focus on.
