Ford Focus LX PCM Advice

My mothers Ford Focus (05 plate) recently died whilst being driven and was towed to her local Ford dealership for repair. They initially diagnosed and replaced the Speedo Head/Instrument Cluster. That failed to fix it and they then diagnosed a faulty PCM module which would have brought the repair bill to £2,000. Instead of replacing the PCM,I sent the part to ECU Doctor to be tested out and they were unable to find anything wrong with it. The garage are still insisting that the PCM module is faulty and needs to be replaced (cost of part alone is over £1,000). I'm after any suggestions as to what to do next, other than asking the garage to replace the part with no guarantee of a fix and no possible refund on the part if it doesn't fix it. Should I advise my mother to cut her losses and simply write the car off?

Thanks

Pete