Hi there - my DD is now 4.5 and was diagnosed just around her fourth birthday, but our nanny started to flag concerns when she was around 2 (no pointing, didn't ask for things). She's a bit different to your DD: more verbal, but less social by the sound of it (she tolerated nursery but I'm not sure she really loved it until she was older and at pre-school with a bit more structure). A heel walker rather than a toe walker
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For us those early suggestions that "something was up" were the hardest bit. I didn't really understand autism (suspect that might be a life-long study...) and because she was so young we just had no inkling of who she would become or what her challenges would be so we tended to assume/fear the worst.
I am very happy with where we are now. She is in mainstream so far without dedicated support (she does get extra support/attention e.g. at drop off, playtime, when they are doing special events at school, etc. but so far hasn't needed more). I know that may well not always be the case, but for now she loves school and is generally a very happy person. She has challenges around change (one-off events, staff absence, etc.) but otherwise she's a happy person and does fine at school so far. There is no reason your daughter can't be happy too.
The thing to remember about autism is that it's a "spiky profile" - I saw this really clearly with another girl in DD's pre-school class who was non-verbal at 2.5 and still at 4.5 she definitely struggles with speech, and she has a lot of sensory issues (doesn't eat most foods) BUT she actually socialises more easily than my DD - at parties I can see her running off and playing with the other kids much more than my DD does. Although DD talked pretty early I think it took her a long time to really communicate: but it also took a long time for me to recognise the difference between speech and communication.
Your daughter will develop and learn and grow. You'll forget about the worries you have now and find new ones - but then those will pass too. It is different but not worse (just like autistic people). You may even start to spot some traits in you or your DH as you learn more about it - and be able to pass on some tips and coping strategies to your DD as she grows.
As for resources, I found Neurotribes a great read (actually a great listen, I got it as an audiobook). It made me feel much more like we are part of a neurodiverse culture, and that feels a more welcoming and inclusive place to be than very medicalised ideas of children with "deficits" (don't get me wrong, I'm not saying there are no challenges, and I know many have more challenges than we do - but I still struggle with "deficit").
I've also found a lot of comfort following autistic people on Twitter (you can search for #actuallyautistic to find autistic people and use #askingautistics to ask questions where you would like an autistic point of view) and on YouTube. I would probably start with Purple Ella as she is autistic herself as are two of her three children, so she has lots of useful tips and insights. She also has a really nice series of discussions with a friend who is also autistic and was selectively mute when younger.
There are also some speech therapists on YouTube with useful videos. I like "Walkie Talkie Speech Therapy" - she has lots of videoed sessions trying to encourage children to talk and she puts captions over to explain what she's doing and why.
In terms of "what to do" I would push for diagnosis so you at least know where you are before she hits school. Make sure you are on all the waiting lists you can be on. Is there any way to access SLT in your area via a drop in? In our area they have "Talking walk-ins" where you can see a SLT "on the day" to talk about how your child is doing (we are actually going to try to use one with our younger DS in a couple of weeks as he isn't saying much yet). If you Google your County/Borough and "speech and language" and "drop in" or "self-refer" or "early years" does anything come up?
In the mean time look up Makaton and PECS and see if either look good for your DD. If you are thinking along the lines of private support we have a service from an ABA company that we Skype with twice a month (called Beam ABA). I have found them very good for ideas for ways to engage our DD and help identify what skills were achievable for her, what was holding her back, and different games and activities we could do with her to help her build those. ABA is quite controversial, but done this way (by us, not very intensively!) I found it useful in identifying what developmental stages were "next" and finding good manageable ways to work on those (breaking stuff down into tiny steps). It's not cheap but it's obviously much cheaper than the hugely intensive interventions that some people do.
It is a really good sign that she loves nursery. Hopefully that means her sensory challenges aren't too severe if she doesn't mind the busy environment, and she is enjoying the variety of different toys and activities that they have there, so that is already a really good base for the rest of her education. Try not to panic. It's a big adjustment and so much to learn - you have to give yourself time. Speech still has plenty of time to come, and it isn't everything anyway - communication is the key but there are many many ways to communicate and you will find one (or more than one!)
Sorry that was very rambling, but hang in there. Sounds like you are doing all the right things. There is a huge amount to wrap your head around and it just takes time, but you will get to a happy place.