But they can't meet her needs. As you e seen from previous responses.
They can't facilitate her to be educated alongside her peers or attend trips alongside her peers.
I'd start with an email to HOY and copy in HT andLA send department.
Dear X,
Thankyou for our conversation on X date.
Thankyou for informing me that despite meeting the required criteria DD was unable attend the reward trip as it required staffing beyond what is usually provided in mainstream school and you didn't have the dedicated Lsa to support her.
Thankyou for also informing me that if after 5 minutes of arriving at school if DD is too anxious to attend you want me to take her home and try again the next session.
Having reflected on what you have said it's very clear you don't have the resources within the school to meet DDs needs and she needs more than is provided within 'normal' mainstream education.
Having read the criteria it is clear DD meets the thread hold for an EHCP assessment. Therefore I am applying for one and you will hear from the LA for evidence in due course. I will supply all the evidence I have of the times she's been unable to attend or access education afforded her peers with the application.
Please acknowledge this email and any further responses or discussions need to be via email or minuted meetings so we can provide this jointly as evidence.
Thankyou for your support.
Xxxxxxx
By stating facts and not questioning what they've said they have no recourse to say something untrue or say you are wrong.
They could untruthfully dispute the email but you've made it clear you have evidence.
If they call you then you need to write notes of the time and date, what was discussed and any agreed outcomes and email them the minutes and ask for them to correct anything they don't agree with. If they change their minds from discussion you can challenge that and ask for clarification of what they are going to do then to support DD.
And good luck. It's a bumpy road if you do t have a good school but once you've been through the process you can name another school on the ehcp. I did and it was the best thing for ds.