It would probably be better to purchase an external hard disk drive with both USB
) connectrs, format it as NTFS on a Windows-based system, enable
NTFS read-write support on the Mac or use a third-party solution
, copy the files over, move the hard disk drive to a PC running Windows, and perform a few spot checks involving the most critical files to verify they can be read successfully and then call the job done.
Another possibility might be to ask the people doing the scanning on the Mac to save the files to a NAS, and then provide her with that when finished.
I am a little unsure why a service bureau would not be able to provide an NTFS-formatted drive with the files on it; it seems to me that even if they were a Mac shop, they would have many customers who used Windows.