Insulin Prescription

No. Insulin must be prescribed, though in a dire emergency the A & E department of a hospital should help.
I have seen messages which include the information that insulin is carried in the hand luggage - you might find that a letter from your doctor stating that your daughter needs insulin, and perhaps giving the details of the ones prescribed will help you in transit and upon arrival. If you know where you will be staying you might be able to find a GP practice close by where you can register and acquaint them with your daughters requirements - I am not sure how you are regarded now but there should be information available as part of your paperwork, which I am sure will be a considerable pile to go through.
I strongly suspect that there will be payments to use the service, that prescriptions will cost money and that you'll be paying for the medication, and maybe even the consultation - my son in law is from the US, but once you have got through the initial stages access to insulin ought to be well organised - one can but hope.
If you are coming to work for an employer used to bringing in people/families from abroad they might have information to assist.
I hope all runs smoothly for you.

I think you may have to pay an initial sum of £1K-£2K?? to join the NHS. Yes, do register with an NHS GP when you arrive if you can. There are private GPs around as well if needed. This link may help: www.gov.uk/healthcare-immigration-application