The high-achieving teenager, who cannot be named for legal reasons, hit out at the teacher last year after repeated bullying and was immediately excluded from the school in Barnet, north London.
However, the girl - referred to only as 'S' - attended a PRU only once before refusing to go back after she found it 'frightening and intimidating', said her barrister, Ian Wise.
Mr Wise told the Master of the Rolls, Sir Anthony Clarke, sitting with Lord Justice Laws and Lady Justice Smith, S had been 'severely bullied' by fellow pupils.
That was probably because of 'language difficulties' she experienced, and it was 'unreasonable' to expect S to attend the PRU, argued the barrister.
He added: 'S is a well-motivated and conscientious child who wants to learn but who is not in school. While at high school she had good reports from her teachers'.
Mr Wise argued Brent LBC, in refusing to put her back in a mainstream classroom, had failed in its Education Act duty to provide her with 'suitable education'.
The barrister pointed to a report from educational psychologist, Mike Davies, which concluded that, had S attended the PRU, it would have been 'very likely that she would have remained isolated and subject to bullying by other children'.
Mr Davies said S 'did not understand the classroom banter and is wound up by it' and concluded that, making her attend the PRU, would be like going 'from the frying pan into the fire'.
However, Peter Oldham, for Brent, argued that the council's policy of requiring expelled pupils to attend a PRU was 'part of a very carefully thought out structure of support'.
Recognising the importance of the case, the Appeal Court judges reserved their decision until a later, unspecified, date.
STRAND NEWS SERVICE