She can't go far. Phone city vets and spca tomorrow.
Edit: may I ask why you took your dog to a concert?
She's been found. Thank god for social media and that friends of friends of friends can see these types of things and act on them.
She's been collected from one of the city vets and is fine!
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Biometrics - its a common practice - De Waal park is a dog park and most people go to the concert with their dog + picnic.
She's usually 100% off leash, but in this case some other aggro dog chased her off and she bolted.