Car purchase gone wrong, what to do?

My granddaughter just bought a car from a young couple for $1200. They have yet to deliver the car as it had to go into the mechanic shop to have a knock looked at. My gd agreed to pay for the mechanic as she was in bad bad need of a car and had the money to do so. It has been over a week and she has not heard from the mechanic or the person she bought the car from (who still has the title). All she has is a bill of sale and a receipt. Can she take this down and file for a lost title and then report the car stolen, or should she just keep trying to contact the seller and mechanic, what should she do? The price agreed upon for the fix was oly $600.. What should she do?