Dear @Laurakiaora Have you ever read the threads on here where someone can hear terrible shouting from their next door neighbours house, and the OP of that thread is asking advice on whether to call the police or not. Nearly always their main concern about calling the police is that their neighbours find out it was them, and then they worry that their neighbours will make life difficult for them, whether the police do or don't walk out of the front door with someone in handcuffs?
The police walked out of your door not looking in the slightest bit worried. Whichever of your neighbours called the police (and I think they were right to do so - it is much better that any incident is checked)
will probably now be feeling a bit embarrassed because they obviously weren't needed in this instance, they might also be worried in case the police think they are trouble makers, so I hope that the police have reassured them on that point.
What I am trying to say here @Laurakiaora is that your neighbour has nothing to feel embarrassed about, and neither do you, so hopefully neither of you will bad about it after a night's sleep. If any of your neighbours are female, and have previously seemed nice, it might be a reasonable idea when you next bump into them to explain about your dear DD to an extent that you feel comfortable with - even if they could give you some emotional support by being empathetic, that could help you a bit.
I agree with most of the other pp that if you were not already so stressed you might have realised that your DD having her hair washed tonight really was not that important. I think (or maybe hope) that if I had had that problem with my ND child when they were a child, I would have probably said something along the lines of
"well when you do want it washing in a few days time, it might take a little longer as the chlorine from the pool water will have made it tangle more than normal, and your scalp will probably be feeling itchy, but with a bit of perseverance we will be able to make you comfortable again"
Obviously, just say it in a matter of fact voice, or even with a slightly sympathetic tone - or if your child would see through that, mine would have done at that age - you could say it more like
"Ok that's fine love, but when you finally come begging me to wash your hair because it is all tangled, smells of old chlorine, and the itchiness is driving you mad, I might help you wash it if I feel like it!"
Of course that sort of ribbing might not work with your DD, but at that age my DC and I often ended up in fits of giggles, but that is probably because I have only really started growing up since my menopause - most outsiders would probably think I was too soft with all of my children...
As I presume you realise, exhaustion and stress (and you have been through far too much stress for at least the last year) take so much out of us, and with the toils your pregnancy is placing on your body, it is not surprising if you can't see the wood for the trees. Also, whether your DD is ND or not, she has pretty much been through the same things as you have, and also knows she is about to have a sibling, but she does not know how that will affect her relationship with you. So with less understanding of why her life has changed so dramatically, I don't think it will be surprising if she starts playing up more anyway. I hope that when she has a full diagnosis, you and she, will get a lot more help and advice.
Have you got any real life support OP, preferably family, or very good friends? If not, then I really think you should be asking for some extra support, starting off with your GP - actually your GP should know that you are having a very hard time whether you have real life support or not. Good luck Laura, you can get through this, you obviously love your DD very much, and having lasted this long you are almost certainly stronger than you realise. Believe it or not, my life actually got quite a bit easier in most respects once I had another child, it certainly affected my mental health in a positive way, maybe partly because with baby number 2 I felt that I could relax more, as I had a lot more idea about what I was doing, and somehow relaxing and feeling more confident with baby number 2, made me relax and feel more confident with baby number 1!