My understanding is that to get an ehcp you have to prove the school can't meet her needs No, it is for children who need considerable support and/or adjustment in order to access their education.
but if they don't recognize her needs in he first place There are recognising her needs though. You say :
She attends small groups weekly for learning, ear defenders to hand, visual timetable, a few sensory breaks. I've been picking her up slightly early to avoid the school run So they are recognising some needs. The issue (if I am reading it correctly) is that her need is greater than the current adjustments. All of this I've been taking her in late to avoid the rush and picking her up at lunchtime for the last week as until we get on top of things I just feel it's all too much for her is evidence that she isn't coping with school at the moment, and therefore needs something more.
This is a positive step I spoke to the senco today finally, we've scheduled a meeting with the educational psychologist for next month.. What I would suggest is that you write out all that you've told us, (plus of course anything you haven't written here) and get that formally minuted.
Let them know about the fact she may be 'holding it all together' for a lot of the school day, but the impact that has on her (wetting herself, not sleeping, etc.).
Ask for a sensory assessment to be done - for example the AET Sensory Assessment, but I'm sure there are others about.
Ask if staff can do an Autism Awareness Course - even an hour / 75mins at an afterschool staff meeting would help (IME SEN/D training on initial Teacher training is really, really limited).
Ask to see the support plans they have in place for her. They should have specific targets for her and a plan of how to help her reach them. This doesn't have to be academic, it can be around minimising her anxieties, around social skills, even around letting school staff know when something is making her anxious.
As she is not completing a full school day, alongside her peers then that is something they should be working towards.
The teacher - who you say on one hand doesn't see an issue, on the other hand is saying that she has communication issues.
Other people who can support you locally are SENDIASS (Put into a search engine with the name of your local authority, Every LA has to provide this support to parents of dc with SEN/D). Try CONTACT (used to be called Contact a Family). Also NAS (National Autistic Society). There are lots of other local groups, specific to individual areas, which can be really useful as other parents can offer lots of local advice for you.