Am I in the wrong not calling the police?

Trigger Warning: this post involves domestic violence.
Last night I was witness to something awful.
This car was driving crazy down my street and then came to a sudden stop in front of my house. The female passenger got out and then the male driver. He was yelling at her, she was crying hysterically and sitting in my neighbor's yard across the street. I was outside, and so was the couple next to me and the guy that lives next to them.
The girl wouldn't get back in the car and the guy takes off. The girl got up and started walking. She was only a house or two down the street when her boyfriend comes driving down the street like crazy again.
The man got out, screaming at her and that's when he grabbed her and was thrashing her around. Honestly, words can hardly describe what he was doing, but she looked like a rag doll and was screaming for her life.
I screamed "get your hands off of her!" as loudly as I could and ran towards them, that's when the man threw her on the ground, got in his car and took off. My neighbors all went inside.
I helped the girl up, and I made sure she was alright. I apologized for being a stranger who was intervening and briefly explained that I was a survivor of an abusive relationship. I know what it feels like to love someone who then tries to kill you. I know that one strangers words will probably not be a catalyst for a women to suddenly leave her abuser and never look back. 
She asked me not to call the cops. I asked her if she had friends or family I could take her too, but she wasn't from my city and doesn't know anyone. And she didn't want me to take her to a shelter. She said she lived just a couple blocks from me and she wanted to walk. I have her my phone number in case she changed her mind about wanting help. 
I urged her to call me day or night bc that man would kill her given the chance. My husband, who wasn't home at the time, was equally proud that I saw something and did something but was also concerned that I just disregarded my own safety and ran towards danger. But I have to say, I'd rather risk my life doing what is right than turning a blind eye as my neighbors did.
So today I've been struggling with my choices. It all happened very fast, and today I just kept thinking I should have gotten that man's license plate, I should have called the cops. But what do you all think?