"Apple Application Support?"

Here's my situation: My mom wanted to free up space for our computer in hopes to improve it's speed, and she just started deleting things (seemingly at random). Two days after this, I turn on the computer and see a message from iTunes saying:

"Apple Application Support was not found.

Apple Application Support is required to run iTunes. Please uninstall iTunes, then install iTunes again.

Error 2 (Windows error 2)"

Sure enough, I can't get into iTunes. I have no idea what the problem is or how to fix it. Could I get a little help here?