Don't know how techie you are, but the best way is to just insert the card in your nook color (I have done this and switched the card from NC to my nook touch and it works) and nook will format it, then use Calibre to put the books on the card (Calibre will show the card in the nook). If you want the book covers to show, follow this thread:
http://bookclubs.barnesandnoble.com/...ssion/N2E-not-
displaying-all-book-covers-in-Library-s-icon-view/td-p/1054606
If your books are DRM locked, you may have to unlock them or they won't open on her nook.
Good Luck!