I know it's a day late and a dollar short but, I've got a folder on my desktop called "BlackBerry Backups". In that folder are two folders for each OS update I've done; the files I removed from the Java folder (in case I take out one too many; which I did once), and my 3rd party apps backup. Each folder is labeled with the OS build.
I have like 12 backup files. Damn storm os updates.
There is no way of telling, which one could be hers.
in the folder on your computer desktop you should be able to right click on the file and go in properties where you should see the files creation date.