The girl is the youngest of four and her family says her older sisters all wore the niqab when they attended the same school, and have succeeded academically.
"This is not a religious issue, it's a human rights issue," said Mohammed Khaliel, a High Wycombe Muslim community leader, speaking for the family.
But he acknowledged that the town's 20,000-strong Muslim community did not, for the most part, support the family's fight.
Attempts are being made to avoid a court case, with both the county council and the school reluctant to pay legal bills estimated to hit pound;500,000. Last year, the Law Lords upheld a Luton school's decision to bar Shabina Begum, a Muslim girl, from wearing a long loose gown, a jilbab, to classes.