What are the documents required to enter KSA by Road

Take both, your friend, and her car with you, express entry, Insurance for Saudi also required, take water bottles, juice, fruit and nuts in you packs . . . .. .. . .. . Enough cash is important .. ... . .. . . .. . .

This is difficult question to answer as it does not take place commonly. It would be better if you could have the isthimara transferred to your name and when you return transfer it back to the owner.

In case if I use someone vechicle what documents should required to bring do you have any idea about this thing ...

You should go in your own car with a valid Istimara in your name. If you travel on someone else's car, you may face problems. It is of course understood that you must have a valid visa.