Being asked to go shopping for a new car might seem innocent enough but be careful.  If the new car has problems, you might be held accountable even if you did not make the selection.  It is called “guilt by association” and it is a lose/lose situation.

And, while you may not be a mechanic, you should have known that the engine was bad.  And, if you did know that the engine was bad and told her so, you should have stopped her from buying the car.

As I said, this is a lose/lose situation.  Avoid it if you can.