1) Fault apart, is the provisional driver covered by insurance despite effectively having broken the law by driving unsupervised (apparently there are mitigating circumstances for this to have happpened)
Depends on the wording of the insurance policy. But for purposes of the law, driver was effectively driving without a licence. This would invalidate most insurance contracts.
2) Is it the case that by driving unsupervised, her insurance company could effectively claim cover was invalid, but cover the claim for the other party against him-her but deny cover for the other parties claim against him-her.
See answer to 1 above, their is now no valid insurance covering the incident, therefore insurance company will not pay out in any capacity.
3) Do the specifics of the accident, and likely judgement-outcome, have any fault-settlement-blame affect the provisional driver's right to cover? That is, if the other driver was obviously at fault, would it be a different case than one that seems to be a shared liability?
In common law, a party while committing a crime cannot claim civil damages from another party arising while committing that crime. Driving without licence counts as committing a crime. So the driver will be liable for any damages if he-she is at fault. Driver will not be able to successfully claim damages of the other party if they are at fault.
4) Has the provisional driver effectively foregone any legal right to compensation or insurance claim by driving unsupervised?
Covered under 3 above.
5) What course of action should the provisional driver take regarding the police (would it be prudent to advise the police and effectively open up to prosecution?) and although insurance company has been notified, haven't yet decided to lodge a claim until they seek legal advice & representation.
He has committed a criminal offence. It would be in his interests to keep the police out of it at all costs. Best for him to settle any bills with the other party privately.