Have to agree with other posters here, just because the nurse was IN the office does not mean that she was sat twiddling her thumbs and watching the clock until home time.
She was likely sorting the myriad admin jobs on her to do list or may have even popped in for something before a final planned visit.
Unfortunately your sister can't expect to call up towards the end of a working day and expect someone to appear within minutes.
I'm surprised at how many people seem to think nhs community staff can run to their beck and call. They can't - they usually have large caseloads and have to manage workload based on clinical need, route planning, clinics and emergencies.
I'm surprised that you're shocked that the nurse wanted to leave work on time, especially considering that she won't be paid for overtime and may also have her own personal responsibilities, such as her own kids to care for.
The hospital and nursing team might have agreed to do home visits but it also has to fit with the available resources at the time - it sounds like they just weren't available and that's not the fault of that nurse.
It's not the nurse's fault your sister does not drive, neither is it her fault that she couldn't get to your nephew. It's a shit situation, I totally recognise that, but there was an alternative.
My advice: complain that the service doesn't meet the needs of its clients, because the fault here is with lack of resources for service provision. Then look for alternative ways to get DN to hospital if it happens again.