@Acey68
I'm surprised how many self-righteous or ignorant posters there are on MN. Some of them are downright vicious, some are downright wrong and some are both!
First, about being over the limit in England:- you are over the legal limit if you have 80mg of alcohol per 100ml of blood or 35 micrograms of alcohol per 100ml of breath. Whether you are over the limit or not depends on how much you weigh, what your metabolism is like, whether you had it with food or on an empty stomach, how stressed or tired you feel and how long ago you last had a drink.
All that business about being over the limit after two small glasses of wine, is just a rule of thumb for an average weight person. Those posters who think the limit is measured in glasses of wine or units, are plain ignorant. You can find "calculators on the internet to help you check whether you are over or under the limit, enter your weight, how much alcohol you had and when you drank the last of the wine. Some calculators will tell you the rough time when you should be OK to drive legally. If that's a couple of hours away, then leave your car keys and get a taxi home.
Unless you are really skinny and thin, two small glasses of wine taken over a period of 3 hours or so with a meal, probably with a coffee afterwards, the chances are good that you were well under the limit.
As for your friend's request. Does she often ask you for rides? Or very rarely or never? My answer would depend on that. If she doesn't usually ask you for a ride, then perhaps she felt afraid to use Uber or public transport on her own, or perhaps she wanted to have a private chat with you about something confidential. There's no black or white answer here either, you have to use your judgement.
When I passed my driving test and bought my very first car, I used to drive it everywhere, including to parties. But the downside was that I wouldn't be able to drink, parties are no fun when you've been on orange juice all evening and everyone else is very merry, and - to top it all - at the end of the party, everyone would be expecting me to give them a lift home. People who've had a few too many are very quick to ask for a ride. Rather inconsiderate of them. I soon got fed up with that, and simply stopped using my car to go anywhere where wine was going to be on the menu - you just end up not enjoying yourself and providing a free taxi service at the end. I completely understand that you said no.
As for your reason for not driving your friend home, that was a poor, lame sounding excuse. You should have explained that you were really tired and just couldn't drive her home tonight. Rather than offering to pay half her fare, you could have asked her, will she have enough money for the Uber, you'll gladly lend her the money if she was short.
I'm assuming that you hadn't offered to drive your friend home beforehand, and that the her request to drive her home was out of the blue.