DVLA registered keeper is the person who is responsible for the vehicle and a point of contact for the insurance companies and the DVLA. However, very clearly note that being a registered keeper DOES NOT make you the owner. The Ownership of the vehicle and the registered keeper are different.
In your case, you are the owner, and merely being the registered keeper does not make your wife the owner.
You have ground to make her pay or in certain circumstances get is reposesed. You will need a local legal advice and it is best advice to follow the local advice that you are getting.
Hope this helps...Warm Regards,