The former head of Downs View school in Brighton sought clarification of the ban.
Ian Poole, of the National Association of Head Teachers, said the terms of headship in the maintained sector were defined, but that was not so in private schools.
He asked for the wording to be changed either to specify a ban on being a state school head or to make clear to Mrs Reed what posts, as a registered teacher, she could hold in the independent sector.
The committee refused to vary the condition, saying there was no uncertainty in the original ruling and that the term "headteacher" was commonly-understood and in everyday use.
Mrs Reed, a head of 26 years experience with special needs children, resigned from Downs View in November 2003. She now works as a teacher.