Pickle Of a Question...

OK have a question for you guys..
I bought FFXIV on steam .. I didn't need the key (don't ask) so I gave it to a friend of mine.
At the time she had downloaded the demo version on steam and was trying it out .. she applied the code in the Mog station and has the full game now.
Today she got on her PC and FFXIV was gone from the steam library.. its still in steam/steamapps/... but the Boot folder for FFXIV is missing.

Does she need to reinstall the entire game over again? or is it possible to transfer the boot folder from another PC to her's?

And why would FFXIV just up and vanish like that off of steam .. even though it was a demo version .. would that be why?
Thanks for any help