I would ask if she had it serviced by the dealer after she quit using it and ask to see the receipt.
I bought a used Bernina 440 with embroidery and the machine was pristine. The embroidery unit had not even been used and was new in the box (confirmed by the stitch count on the machine). The embroidery unit had a factory defect - a bad board that cost me $400 to replace (warranty does not transfer from original owner). It has worked great since (5 years now). I got a great price, but after that it wasn't a great deal, just an average one.
The moral is make sure is is checked by a dealer and everything works fine. Otherwise it can be an expensive lesson.