"When I got to the school they said to me I can't help Tammy," Harrison said.
"They told me I couldn't help her because of insurance and child protection, so obviously I wondered and asked how she was going to take part.
"Last year she was able to come out of the buggy and walk with me carrying her. When she does that she feels like she's joining in and she enjoys it more. It also gives her more exercise which is really good for her.
"But they told me [if she was to take part] her one-to-one would have to push her around in her wheelchair buggy."
The school told Harrison that Tammy's teacher was the only one allowed to assist the 6-year-old during the race, a stance that left the mother furious.
She told Cambridgeshire Live other parents watching on were disgusted at the school's stance.
"I said no I will take her out and help her do it. She is my daughter and she needs my help. All the other children were taking part and she wasn't.
"I don't understand. When it suits them [the school] I can go in and help them lift her to use the toilet, but when it suits Tammy I can't do it.
"If I wasn't there, she would have had to stay in her buggy and imagine how she felt, sat in her buggy thinking 'look at all my peers and I am left here sat in my wheelchair.'
"Her one-to-one even gave her the option and she said I want mummy to help me do it. But the school never gave her that option."
Harrison was told to leave following the incident, to which she refused, telling the school she was staying to help her daughter.
She says she feels discriminated against, but apologised to other parents who may have objected to her stance on the day.
The headteacher of Jeavons Wood Primary School, Sue Wright, issued a statement regarding the incident, also requesting that the story should not be published.
She said: "If a parent is upset by a decision taken by the school then we have procedures in place to address those concerns.
"We always try and solve any issues informally but there is a clear complaints procedure to follow if they are not resolved.
"No parent has contacted the school informally or formally to make a complaint about sports day."
She also said the school cares very much about Tammy's welfare, and that they did not intend to embarrass her.