This was not a good friend. It was a neighbour - so a loose contact. When you ask a loose contact/neighbour/colleague to do you a favour which involves them spending their own money, you ensure you RAPIDLY repay them and thank them for their kindness. It does not matter if it is £1 or £100.
It is poor form and rude behaviour to have either not quickly paid the money back or not made contact to explain when it will be appearing and apologise for the delay. OP is not being churlish or mean in wondering where the money or this contact is.
Personally, I would send a message by text or drop a note through the door with the bank details as an alternative if cash is tricky. However, you shouldn’t have to do this.
If this were a good friend, things would be quite different. However, it is this kind of response to a neighbourly kindness that makes people not offer or think twice about helping someone out.
Some people are lacking in social skills. They don’t seem to realise that you pay a neighbour back speedily or make contact to explain a delay, regardless of the amount of money. Clearly from the responses on this thread, some people decide that is a sum of money is small, it doesn’t need re-paying, or that if someone offers it, it should be turned down.
Essentially, this neighbour has now put herself in a position where it will be very hard to ask Op for help again, or if she does, Op really will think twice. She certainly will struggle to ask for more significant help with a positive response.
If I had shopped for a neighbour, I would expect them to bring me or arrange to repay the money speedily regardless of amount. If it was a small amount, I might be happy to say there was no need, but Iwoukd take it when offered, because I understand that the nature of neighbourly favour isn’t quite the same as that between good friends. Often someone only feels they can ask for the favour if they are sure they will be able to repay the money spent, or return the favour. To refuse to accept the money could make the neighbour feel awkward or as if they could never ask again.
Certainly ask for the money. It doesnt have to be done in a snipey way. And if the money is quickly forthcoming, just move on and forget about it. But if it’s still not forthcoming or some communication about it, I probably would feel quite annoyed about it. It really isn’t about the sum, but simply that if you ask a relative stranger to spend their own money for you, regardless if the sum, you ensure you repay it quickly.