I is all a matter of opinion. 99% of lactation consultants will tell you to feed on demand (let the baby tell you when it is time to eat). They have a hard time with this book because it tells you to try to take note of the length of time between feedings so you can feed on more of a schedule. That is their only reason for discreaditing the book.
My first lesson in parenting was on day one. A nurse told me I couldn't give tylenol to my baby who was circumsised just moments before. The mommy instinct in me hit the roof. I told her, "He is my baby I can make that choice on his bahalf, because you don't think it is a good idea does not mean I don't have the final say."
Let her read the book, talk to others who have read the book and followed it and allow her to decide for herself.
I followed the ideas in Baby Wise but not to a tee. It did help me set a guideline for what I should look for and I will tell you it did bring peace and order to our home!
Since then I have read Toddler Wise (reading it again now), Preschool wise and Child Wise (this is the best one- you will definately re-read this one).
Hear what others say but you be the final judge!
Thumbs up for Baby Wise!