Is she a member of either the AA or RAC, if so suggest she speaks to them. Having a camper van she most likely is connected to the RAC, the same are well connected with the Caravan and Camping Club of UK.
There must be a 'professional body' they could be reported to or the OFT? Can understand you don't want to do it but as a good citizen you could advise her to?
My advice would be to send her to the citizens advice bureau with a copy of her original receipt and a letter from yourself explaining the cost differences. They would be the best people to advise on the best route to take.
