you need to be very careful, if you let her use it without conditions and she has the high res version then she has the right to market that picture.
while it is flattering to be asked (i have a few times), you have running costs (your gear and getting to the shoot).
you could regret letting her have it FOC latter.
as a minimum she should have a small low res for cards and specifically has no resale rights. also you should stipulate that the printer has no rights to use this picture for other clients.
get details of printer and her details before you hand over.