When we make general assumptions about the reasons a parent may have for behaviors, we hurt our ability to offer support. Were it me I would clarify first whether the mother was given information regarding some sort of schedule. Mothers who are less than sure, or scared for the well being of their baby, feeling ill themselves, unsupported, confused, suffering from the beginnings of ppd or other things may be too overwhelmed to go outside of dr's orders. It is the offering of nonjudgmental evidence and information to the new parent where we make the greatest change.
Just another perspective, we can see you feel strongly about the matter.