I work in a secondary mainstream school and I'd be surprised if your DD's school can accommodate this. This is not to say that your DD doesn't need it, or that school wouldn't want to do it, or that the OT shouldn't have 'prescribed it'.
There's a lot of expectations of what schools should and shouldn't do, when the reality is that the main business of a school is education, and even budgets for that are dwindling.
I also don't mean to say that OT and other therapies shouldn't happen in school. It makes sense that they do. However, the reality is that there's no budget to build in the appropriate spaces that are necessary for this, equipment, and appropriately trained and paid TAs that are available for 1 to 1 support, as most spend a lot of their time supervising large numbers of children, and focusing on behaviour, crowd control, or on 1 to 1 support with kids who do have a EHCP, which are very very few.
I agree with previous posters that it's very unlikely that your DD will get an EHCP on this basis. The very few students that have an EHCP in the school where I'm at have extremely complex backgrounds, diagnosis and needs.
Even if your school agree to this, how can you be sure that the person allocated to carry this out is even trained on neurodiversity, sensory challenges, etc., and that won't do more harm than good?
This is similar to GPs telling parents that their kids' mental health problems will be supported at school, and then school will appoint a wellbeing officer who has no mental health training and is probably doing that job because it's term time only (absolutely nothing wrong with that), and there's a student with serious psychological distress being supported by some random who will likely try their best but feel overwhelmed at the enormity of what they're taken on, be wholly unsupported, and likely not to make an impact, which is a better outcome than the possibility of making a negative impact, which is the risk when untrained people are appointed to provide such supports.