I have 2 autistic DC (DS9 & DD6). This is what I wish I'd know earlier:
It will be fine, really it will.
It will be hard at times, and your parenting journey will look different to what you imagined, but it won't be nearly as bad as the 1000 what if's you currently have running through your head.
Get support now - I put it off too long, as I felt like an imposter accessing services when my DC's difficulties arn't as server as other. But it really helps going to groups so DD grows up with friends who are like her. It also helps me as DC got older, as the other parent their arn't going judge you dealing with a meltdown, as they've been there too.
Put her into a school nursery as soon as you can, and start the EHCP process. Technically you can ask any nursery to start it, but in my experience, having access to the school senco was helpful as they have more of ab eye of what support she might need through school.
Give yourself permission to do things that work for you. - If she doesn't like playgroup or softplay, it's not mandatory. I spent way to long dragging my autistic toddler to thing they 'should' like. If she wants to were crocs every day, no one will die if you let her. If non of her safe foods are normal breakfast food, fish fingers a 8am is better then going out hungry.
Work out her sensory profile and get all the things. My 9yo bounces on a gym ball while he's watching TV, as the movement keeps him regulated, and having a safe outlet stops him climbing on and jumping off my furniture. My 6yo is all about sound and texture, hours of play with water, dogh or sand, and a ridiculous range of instruments keeps her centred.