Alison Waldock, 51, 'forgot' the seven-year-old dietary needs when she asked if the schoolgirl wanted gammon and the youngster said yes.
The school's headteacher spotted the mistake as the youngster was about to tuck into the meat and swept the plate away from her.
The girl's parents were then told how close their daughter had come to eating the meat, which is banned in their religion.
They complained to the school's catering firm and Ms Waldock, a dinner lady for 11 years, was suspended pending an investigation.
She insisted she had made an honest mistake and had simply lost track of all the dietary requirements of the children at Queen Edith Primary School in Cambridge.
But she was dismissed a month later for gross misconduct due to 'negligence, carelessness or idleness'.
Alison Waldock,51 - sacked for honest mistake
Ms Waldock, a mother-of-two, said: 'I feel the school and catering company made me a scapegoat so they can't be seen as politically incorrect.'
'I was really upset when I found out what I'd done. I'd never have done something like this on purpose. It was a simple mistake - I was so gutted with the school's reaction.
'I'm now too scared to take any similar catering jobs with the council.
'I don't think I will ever work as a dinner lady again. I don't want to go through all this again - it has been horrible.'
Ms Waldock, of Cambridge, added there were around 40 pupils with various dietary requirements and it was impossible to keep track of them with the lists she was given.
Ms Waldock said she immediately apologised after realising her error.
She said: 'I went out and apologised to the headteacher, who was obviously annoyed. I said I was sorry and that it was a mistake.
'A week later there was an investigation and I was told that the school did not want me on site.
'I was gobsmacked. I haven't been back since. I feel so let down by the school. I had worked there a long time. I just made a mistake and I am sorry.'
Lunchtime UK operations director Peter McAleese said: 'Anyone losing their job is regretful. But there was a full and transparent procedure that Alison went through - as well as an appeals procedure which she lost.'
A spokesperson for Lunchtime UK added: 'Following an incident involving Alison Waldock at one of our schools a full investigation was carried out prior to suspending her on full pay.
'A standard disciplinary procedure ensured which resulted in Alison Waldock being dismissed for gross misconduct.
'She was represented by the GMB union throughout the whole procedure and is now entitled to appeal through the tribunal system.'
But headteacher of Queen Edith Primary School said this was not the first time Ms Waldock had made a mistake over pupils' dietary requirements.
Head Teacher Caroline Peet, said: 'We understand from Lunchtime UK that this was not a one off event and due to the significant number of children involved the company treated the issue with the seriousness it deserved.
'As her employer it was wholly up to Lunchtime UK to decide what appropriate action to take.
'The school reflects and celebrates the diverse cultures that make up the community it serves and respects the beliefs and values of our children and parents.'
UKIP leader Nigel Farage said: 'I feel desperately sorry for her. If she'd served gammon to a vegetarian would she have been fired? I think not.'
This story shows the kind of country we now live in.
We are infested with PC do-gooders, who will go out of their way to punish anyone that does anything that does not fit with their political correct agenda (even if it was a mistake).
I wonder what would happen if the parents of a Christian child instructed that their son / daughter was not allowed Halal meat and he / she was accidentally served it, would this result in a sacking? - I will let you decide!