My first question is: why does you friend think her baby is constipated?? Breastfed babies VERY rarely get constipated, as breastmilk is a natural laxative, and babies under 6 months of age should NEVER be given additional water! They are very susceptible to what's essentially water poisoning. Breastmilk is actually mostly water, so they don't need additional fluids until they aren't exclusively breastfeeding anymore.
That being said, I'm curious to know why your friend thinks her baby is constipated. Is he having trouble pooping? Is he straining or struggling? Does he seem uncomfortable? Are his poops hard/firm or more like an adult's stools? If the answer to these questions is no, then he's not constipated. Believe it or not, it's actually very normal for an exclusively breastfed baby to go DAYS without stooling! Dr. Jack Newman, who is the foremost leader in breastfeeeding, said that the longest he's seen a breastfed baby go without stooling is 31 days!!!! (I was amazed, too!) As long as baby is happy, content, and doesn't seem to be uncomfortable when stooling, he's not constipated. If he's not happy or content, etc, then he may be.
My next question would be: how educated is your friend's pediatrician about breastfeeding? Unfortunately, breastfeeding is NOT part of a doctor's medical training, so if they want information and education regarding breastfeeding, they have to do this on their own. Sadly, many pediatricians know next to nothing about breastfeeding, and the wrong advise could be given.
Your friend is more than welcome to use Nursing Mothers Counsel as a resource should she have any other breastfeeding questions or dilemmas :) Our hotline number is (650) 327-MILK, or she can visit our website at http://www.nursingmothers.org. We are a non-profit organization who provides FREE one-on-one peer counseling to breastfeeding mamas at ALL stages, prenatal through toddler through weaning!