And definitely a on the blind deletion thing.
Sorry, I meant that you would also be on the phone with her while that was being done.
is 15 gb
You: Don't delete that
You: OK, open that folder
Her: 'The Mighty Mighty Bosstones'? I don't like them any more
You: Highlight that folder and delete it
... and so on
If there is seriously 70 gb of data on that machine and she doesn't know what it could be there better be SOMETHING that can be safely deleted.
To put it a different way: What can take up that much space? Music, video, games, and maybe a few programs. If she's not a music or video collector and her Users\Whoever\Video folder is overflowing it's a safe bet you can find something in there that can be deleted.
If she doesn't want to delete The Mighty Mighty Bosstones or anything else, it's time to invest in an external HDD.