score:8
Your aunt has to look up her insurance contract. Not every insurance covers occasional drivers. There are basically 3 categories of drivers insurance wise :
The usual driver of the car and insurance holder.
Someone who is registered in the contract as a regular driver of the car (partner, family member, etc.) but not the main one. Not your case.
This is you - anyone not specifically mentioned in the contract who happens to drive the car. Oftentimes in case of accident, the excess will be higher if they were driving. In France, I never had an insurance that doesn't allow them, but I know some cheap contracts have a driver restriction to only principal and secondary drivers or charge prohibitive excesses in case of accident caused by an occasional driver.
Upvote:2
Note that most European countries insure the car, not the driver (as in the US). That implies that anyone driving it is insured (if he has a valid license).
You can verify that for France by googling, but if she has the car insured (which you see by 'does it have a sticker on the plate/window'), any legal driver is insured with it.
Upvote:6
French law provides that damages to others created while using the vehicle have to be covered by compulsory third-party/liability vehicle insurance, no matter who is the driver. This is provided for by article L211-1 of the Code des assurances:
Les contrats d'assurance couvrant la responsabilité mentionnée au premier alinéa du présent article doivent également couvrir la responsabilité civile de toute personne ayant la garde ou la conduite, même non autorisée, du véhicule, à l'exception des professionnels de la réparation, de la vente et du contrôle de l'automobile, ainsi que la responsabilité civile des passagers du véhicule objet de l'assurance.
Note that it even covers non-authorised use of the vehicle (say joyriding). But it does not cover damages to the vehicle itself (only mandatory liability insurance) or to unauthorised drivers (not relevant here). This also assumes that you do not drive the vehicle so often as to effectively be the main driver, for the contract could then be void and you could be found guilty of fraud.
As explained by guillaume31, the contract can also include a special excess clause for other drivers so an accident could become expensive but you can be confident that you are not driving illegally without insurance or on the hook for large liability payments (bodily injury, etc.) So if you find a green sticker on the windshield (with the right dates on it), you can be confident that the vehicle is insured and that this insurance technically covers any driver.
As far as I know, clauses limiting coverage to named drivers are very uncommon in run-of-the-mill insurance contracts, unless your aunt explicitly sought a cheaper “conduite exclusive” insurance contract. In that case, having an accident could also impact your aunt's no-claim benefit.
Also, here are few French phrases that might useful when looking for additional information: