She would not pay a deductable when a 3rd party is making a claim. However, if you were to make a claim against your policy, you would have to pay your deductable (probably more than the cost of the repair), and then wait for her carrrier to reimburse the deductable. Probably better to have her deal with her carrier and get an agreed-upon cost of the repair, i.e., you can get an estimate from a shop of your choice and then submit it to her carrier. Assuming she wants to go through her carrier, they will set up a claim and assign a claims adjuster and claim number to the claim - normally, recovery is not a big deal with this type of claim because there is no issue of liability (i.e., clearly her son's fault).