The thing to keep in mind is that autistic folks experience the world differently to neurotypical folks, and as someone pointed out, sensory discomfort can be genuinely painful. It’s hard to wrap your head around if you’re neurotypical but just imagine this: it’s Christmas Eve, you’re sat on your sofa relaxing expecting to spend it alone, and the shops have just closed - then, your family call you and tell you that they’ll be over at 8am the following day. Nothing is ready, and you have no way of preparing. That’s what life can feel like for a person with autism - a constant sense of impending *something* and feeling like you’re out of the loop. That’s enough to cause anyone anxiety and tantrums.
I have an autistic son and one with ADHD, and I have ADHD myself, so whilst I’m no expert i do have a fair bit of experience in raising ND kids and in being ND myself.
It is really challenging sometimes - my eldest struggles a lot with school (it’s very common for autistic kids to find it very hard to have their time taken up doing things they don’t enjoy - nobody loves going to school but for an autistic person, it can feel like being robbed - they would rather be spending time on their special interests than being forced to endure a sensory and emotional nightmare for 6 hours a day five days a week). You may find that once you have had her assessed and diagnosed, and she can receive the reasonable adjustments she’s legally entitled to at school, it may make things easier for her and therefore you. My sons school will sometimes let him take a month off of doing homework (school needing to stay out of the home is a very common need for autistic kids) and it makes a big difference to how adaptable he is elsewhere in his life.
When things are stressful and challenging and I find myself feeling so helpless that I just find myself wishing that things were different and that my parenting journey was easier, I remember that my autistic sons gentleness, creativity, kindness, openness, empathy and just the beautiful way he sees the world isn’t the problem - the problem is that the world he’s forced to live in isn’t set up for people like him, THAT is the challenge. I hope we are moving toward a kinder world in which autistic people are automatically considered and accommodated at a base structural level but until then, you’re doing the right thing by looking into assessment. If waiting for an NHS assessment isn’t possible and you can afford it, check out the registered assessors on the NAS website and look into getting an EHCP so your daughter gets the support she needs at school - if your school aren’t forthcoming about assessment and support you may need the latter (and you don’t need an official diagnosis to get an EHCP). Good luck!