Yes. Since you are married, she can deduct the expenses for a car that is your vehicle when you are filing a joint return.
However, you cannot guess at the mileage. You do need to have it written down. It is possibly that you would be able to get this information from DoorDash, or you could get it from using something like Google Maps timeline to see where all she has been and then break it down between DoorDash and personal. If you cannot find her actual mileage than you can claim actual expenses.
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