There is actually a very easy fix for this.
When you install the program, Windows sets permissions on the folder. Typically, they are set for "Everyone".
What you can do is right click the program's folder under Program Files, and go to properties. Then hit the "Security" tab and take out "Users" or "Everyone" (Could be both.)
After you do that, add YOUR account and give fill permissions. That way, you will be the only one to access that folder, and your sister won't be able to.