Your wife did not have the use of a courtesy car that is given free out of 'courtesy, instead you had the use of a credit hire vehicle, which you must have entered into a formal contract with. You are right to be concerned, without knowing what you have agreed to opens you up to a whole plethora of issues. If you had the hire vehicle for an extended period of time due to poor repairs, the repairer is liable for the cost of that hire from the original date of completion to the time was vehicle was rectified.

The at fault insurer is not liable for this. You need to be very specific in your language, did you deal with your insurer who passed you to an accident management company? Or did the insurer arrange repairs while arranging the credit hire? Or have you arranged your own accident management company to assist you?