Best bet is to buy another hard drive,
just a (used and cheap) spare, just big enough to fit the contents of her C:\ drive.
install the new harddrive and ghost her C:\ to the new disk using
ghost.
Then you can wipe the existing hard drive then repartition it using FDISK,
make 2 partitions this time on the hard drive one for C:\ and the other is D:\
You can make them whatever sizes you want,
I usually don't make C:\ any bigger than 5 GB depending on what version of windows and how big the disk is. The rest of the disk (D:\) is for user files, think of it as a separate drive lettter for "My Documents"
Now just restore the new C:\ partition from the ghost file you created on the (new) spare disk.
The beauty of this setup is that once you have the partitions in place you can "ghost" the state of C:\ to a file it creates on D:\ which is the separate partition of the same hard drive. Then at anytime you can just boot into dos from floppy and restore C:\ from any ghost file you have on D:\
HTML manual for using ghost can be found here :
http://davecosta.com/software/ghostmanual.htm