It would be best if you have your daughter-in-law's PRS-650 on hand. That way, you can use Calibre like you normally do. Just connect your daughter-in-law's 650 to your computer, select the books you want to copy, click on send to device and that's it.
If she just gives you her SD card, then you can use the
Save to disk feature. Do you have a card reader installed on your computer?