Not technically, doc. It IS her car.
At some point, nickpfc63, decided to do the car up. He ought to have informed the owner before he touched it..........
If she, owing no monies, believed that the car had been scrapped (after instructing so) on a particular date(ish); I find it difficult to believe that any court in the land will grant the OP any sort of retrospective storage costs. There was no contract to that effect.
It may be covered in OPs T&C in which case he needs to see a solicitor to have a formal letter to that effect sent.
Until, such a time as the owner relinquishes said ownership..........it is HER car !! Ownership can only be assumed in a particular manner after fulfillment of a particular set of conditions.................this ain't one of those situations !