Having gone through this for years with my ND teenager, I learnt many things.
Worrying about upsetting school staff gets you nowhere. Instead, the business like, detached, professional and assertive, yet polite approach is absolutely essential. Schools are overwhelmed atm, I believe moral is probably low for teachers having to deal with so much including a huge number of Neuro divergent kids with not much extra resource to manage their needs.
This means you will not get the absolutely necessary support your daughter needs with the ' oh please thank you, sorry to bother you approach'. I used to do this until I realised in such a difficult way.
You have strong suspicions she's Autistic. Don't ever back down on this in conversation with anyone in school or medical professionals. . Systemic gaslighting by schools and GPs is horrendous. I experienced it, I speak to many going through it now. In the end we had to pay and he is obviously ND in multiple obvious ways.
Your meeting in April - you will need to ask to meet the SENCO and class teacher.
At this meeting I would ask for your daughter to be placed on the SEN register. She doesn't need a diagnosis for this. The school will know. Ask for the school to work with you in the development of a basic SEN plan. This needs to include establishing needs in school and writing them down. One such need is social anxiety, particularly regarding lunchtimes. What exactly will school do to accommodate this? A TA? A buddy system? If there's an issue with food avoidance then obviously this needs supporting properly. The school need to assess and identify all needs.
What else is she struggling with. It won't be just this. And what exactly will they do to identify every need and then outline exactly how they'll support it? That's what the SEN plan is for. They won't have one. You'll need to remind them they should do this.
With the Autism/ ADHD assessment - exactly who is the assessing body for your area? When will they submit an application to assess? And you will need to submit your supporting info as part of it. The NHS tend to commission a third party organisation yo do the assessments. They don't do these easily. You need to push and have evidence to even get them to agree to assess.
So the above is important to ask in the meeting. It's important to note down everything then email it back to them exactly what agreed at the meeting.
Come secondary school, things can become incredibly stressful, distressing and a nightmare if things aren't set in motion now. Never trust a school who says they're doing something without specific defined detail as I've highlighted above.
You could for now write an email about April's meeting forewarning what you'd like to discuss. Eg. SEN plan, assessing needs and establishing accommodations and confirming details ref the AUTISM assessment. You could add one line at the end saying you're particularly keen to discuss issues regarding lunchtime eating as part of this. It has become apparent daughter is eating in the toilets etc etc.
Do it in one brief email like this. If you keep emailing bit parts it misses the bigger picture and you get lost in the category as that parent. The bigger picture is what I've highlighted in the beginning; SEN plan and Autism assessment. What when, how basically. Then tag on your concern ref lunchtime. They'll do something about it if they get an email demonstrating your awareness of the system, their obligations and that you are assertive! 🙏