I know she says that - but it's a myth. Recently saw an allergist myself and discussed this - see also this:
**Many believe that blueberries fall under the "no berries until after age 12 months old" rule. Blueberries are not really a common allergen - they are not in the "berry" family. Blueberries are related to cranberries - cranberries appear on many lists of "least allergenic foods" Blueberries are not related to strawberries, raspberries and the like. Those "true" berries may be mild to highly allergenic. In the book, Managing Allergy and Intolerance in the Allergic Infant (published for Health Care Professionals and The General Public), blueberries are recommended between 6-9 months old. There are also several other pediatric allergy books that say that blueberries are ok from 6-9 months old as well.
Unfortunately, a lot of the info in Super Baby Food is off on allergy side.