You couldn’t have taken her in your car – you would have got yourself in trouble.
I think you did the right thing in the circumstances. A LOT of people would have just kept walking.
I would have stayed at the park, phoned the police and kept watch to make sure she was ok. I never trust the police to turn up within a decent amount of time – it could have been ages before they could get there, wouldn’t surprise me that they had all moved on by then.
You did say the boys seemed concerned about her – hold on to that thought.