If it's only a small scratch, it would also be a good idea, as has already been suggested, to contact the woman and ask if she would consider doing it privately. If she agrees, she will no doubt produce a very expensive quote. You can then either just pay up (even a scratch can easily be in the three-figure range, but weigh it up against losing your NCB and paying hundreds more for your policy), or you can refuse the extortionate price she may quote, and say you would like to go through insurance, which is your right and she can do nothing about that.
If she rejects your proposal to do it privately, or you decide in the end to go through insurance, you should contact your insurer immediately. Tell them what happened and the extent of the damage. State explicitly that she was not injured, to preempt any fraudulent whiplash claims she may make. Also state in enormous bold letters that you are not making a claim, seeing as your car was not damaged so you have nothing to claim for; shout that you are merely fulfilling your obligation to inform them of an incident.*
It would also help if you had taken any photos. But if not, and if you have the woman's address, you can go round there and take photos of her car; if it is parked on a public street, she can do nothing to stop you. Do it asap before she incurs any additional damage and tries to put that all in the claim against you, which drivers regularly do (e.g. having a scratch, then taking the opportunity to claim for the massive dent down the side which you've had for years from when you drove into a ditch).
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* I say this because it worked for me. I was wrongly accused of scratching my neighbour's car. He had a white scratch down his car and my car is white; and my car had a scratch in a corresponding place from when I had been scratched years ago in a car park with no note etc. from whoever did it. I knew I hadn't scratched my neighbour's car, he wanted to sort it privately, so I let him get a quote, which was extortionate, so I said no and to go through the insurer. I contacted my insurer, shouted at them that I was NOT making a claim, but just informing them of the accusation, and sent them photos of both our cars. I then found pictures taken of my car several years before which had the same scratch, proving that the scratch had already been there. That was 2 years ago and I've never heard anything back since, and I have stayed with the same insurer and they gave me NCB that year, so obviously they told my neighbour to f off once they'd seen the photo that the scratches to my car were already there! There were several other white cars on the street, and one with a scratch in the same place, but he didn't even ask them, he picked on me because he thought I'd be a pushover as I was young. Lol at him.