Vandelism to a vehicle

The happened in Clackamas, Oregon. I own a business and yesterday a patron left my establishment and 15min later returned saying one of my other customers had scratched there something into her door. She is asking me to cover her deductible because the damage was done while parked on my lot. She never saw anyone do the damage nor did we, however she claims my lot is where it had to happen. Anyway my question is there any liability on my part to her, i.e. do I need to pay her deductible?

Thank you in advance (and sorry for spelling Vandalism incorrectly in the subject.)

I don't see how you could be liable, but you could always report it to your insurance company and let THEM deny the claim.