If the rented car is a covered auto on the insured's policy, then you are right that the permissive driver/daughter has coverage. Now, if the daughter has her own policy, she is the named insured, and the named insured is an insured for the use of any auto, rented or not. The standard PAP states that any insurance provided for a vehicle not owned by the named insured is excess over any other collectible insurance. So, the daughter's coverage is excess under her policy. However, your insured's policy says the same thing—excess coverage for a nonowned vehicle. Now both policies cannot be excess so as to deny the insured any coverage, so the payment for the loss has to be shared, and that share is on a pro rata basis.