Plug it into a higher numbered SATA port and you should have no trouble. The BIOS will still boot first from your disk and once booted Linux will see the second disk as /dev/sdb. You can then manually proceed to mount it:
# mkdir -p /mnt/windows
# mount /dev/sdb1 /mnt/windows
Having said that, the right thing to do would be to tell your wife to take a chill pill and put it in the new machine where 7 will immediately see it and make it available.
Alternatively just get her one of these
and you don't even have to open the case.