Strangely I am in the same situation - vet 2 miles away and I don't drive either. Remember the vets are on the end of a phone and will guide you through what to do in an emergency
I must admit it does concern me that should something happen my boys may have to suffer a few more minutes pain than if I could drive, but then again there are lots of people who do not live so close to a vet surgery and it would take them some time to get their pets to the vets so maybe they wouldn't - I think you have to try and see the 'flip side' to your situation. Coco could not not be in a more caring, loving home and I know you would get her to the vet as soon as you could should something happen - that is all any of us can do
Try not to dwell on what might happen as chances are they won't and also remember that if they do you are more than capable of dealing with it. It may help to have an 'emergency' envelope with some money and phone numbers of the vet and friends/taxi's that you can keep to hand.