Is it registered to her?
Does she have any money?
OK. I suppose she has no assets?
No. If the car is registered to her then she is entitled to physical possession of the vehicle.
It cannot be lawfully reclaimed.
What you can do though is sue her for the money that she owes.
Obviously you may not be able to recover if she has no money but at least she will have a CCJ which will create an incentive to pay.
It is a small claims court sum so it would be cheap to issue and claim.
Can I clarify anything for you?
If the owed about is £7500 then probably about £300- £500.
No problem. All the best. Please remember to rate my answer.