TBH I think she is silly for trying to buy a tatty car and expect it to be fixed up FOC to be a good car instead, and I think she is actually a fucking idiot for taking the car before the faults were rectified after it was agreed they would be, especially as that now means they can easily claim further damage done since the agreement made etc.
Could try citizens advice though for putting together an official looking letter to ask for rectification of the issues as per the receipt.