My apologies. It was indeed another poster that said she couldn't be sued due to her age. You then said, "You’d be hard pressed to argue this as a case of negligence. It was an accident." Given that, as you have said in your more recent posts, we don't know the details of this accident, that is an optimistic conclusion to say the least.
The driver stayed at the scene long enough to get OP's daughter's details. She didn't ask for his details and, according to OP, was uninjured. He was therefore not required to stay any longer. He did not need to call the police (who may not have attended anyway for a minor incident like this), nor did he need to take time to establish fault.
If it goes to court, it will, like most RTA cases, be his word against hers. If she was riding on the pavement, that will go against OP's daughter. If she was in a cycle lane there would almost certainly have been give way markings, so that will go against OP's daughter. If she went into the side of the car, that is likely to go against OP's daughter. These are all "if" - we don't know from OP's posts whether any of them are correct. However, he may well feel he has enough to convince the court that, on the balance of probabilities, she was at fault.
And no, he wouldn't have to explain why he left the scene. That is not in any way relevant to the question of liability, which is the only thing the court would look at.