Homeless dog

I was walking this afternoon in Islington and I saw a dog in a leash walking freely in front of Pret or Starbucks (can't remember exactly) near the station. I thought the dog was owned by some people sitting at the park but it walked towards the woman lying on the floor in front of the coffee shop. The woman looked drunk and was knocked out and the dog was standing next to her. I felt so sad because the dog seemed confused and it was raining. I stopped, looked at the dog, and went on my way. I did nothing. Hours have passed and I am still feeling guilty thinking I should have done something.

What should be done in this situation? I know homeless people take good care of their pets and by the looks of it, this particular dog seemed healthy. I wanted to be respectful of their boundaries as well.