Some states insurance laws require third party insurance claims to pay for a similar vehicle as to the one being repaired. For example in Colorado since July 2004 insurers are required to pay for rental vehicles and collision damage waiver to third-party liability claimants.
The CO Department of Insurance states that the insurance company in this situation should pay reasonable rental expenses for a vehicle comparable to the vehicle that was damaged in the accident. "Comparable" is considered to be similar and may not be the exact make or model.
We are not aware of any such regulation in California. When there is not a state law mandating that a third party claim pay for comparable rental car then it is usually up to the insurance company's guidelines and the at-fault party's insurance policy.
Most states only require with a third party claim that a rental car to be provided due to the drivers "loss of use" of their own vehicle when it is being repaired. The type of vehicle is normally restricted to what you can rent for the amount the insurance company makes available to you which normally is a flat amount such as $25 per day. If you want to rent a bigger vehicle then normally you will have to pay the difference yourself.
The CA Department of Insurance should be able to give you more information on this topic.