My son (27 months old) has had the flu shot 2 years now.  The first year he had no reaction at all.  The second year (this year) he seemed to have a slight cold.  I have never upped his cortef dose with any immunizations.  He as a matter of fact never had any bad reactions to any of the immunizations.  However, my first son (non CAH) was affected by almost all of the immunizations.  So maybe every child handles them differently.  I guess I should add that if my CAH son had had a bad reaction to one of them I would have tripled his cortef and given him tylenol.  I hope this helps.  I guess the bottom line is that NO it is not necessary to up her dose.  I kind of ramlbed there, sorry.