I attempted the download from IE and it was successful.
She had been prompted by another tech to download AVG free edition, but as this download is technically hosted on cnet.com (here: http://download.cnet.com/Avast-Free-Antivirus/3000-2239_4-10019223.html?part=dl-85737&subj=dl&tag=button), she was getting blocked and re-routed to the sc.edu website by SafeConnect.
I tried to grant her temporary Open Access but this failed (she continued to get the re-direct even after opening a new browser session). I also tried to grant a temporary "Guest Pass" in SafeConnect, but when doing this the user gets a new authentication screen, and for this, AD credentials do not work---I have tested it.
Finally the "lightbulb" went off, and I had her connect to the AT&T wifi network. She opened a new browser session, and I directed her to Roaming on their splash page, and then had her select "USC." She was then able to login using her USC network username and password. I guided her to the aforementioned cnet link and she was able to download AVG Free successfully.
After the call I did some testing with Internet Explorer. It looks like the problem with the Trend Download was actually due to stringent Privacy Settings. The download was successful only after changing the setting to Medium (medium-high, high and "block all cookies" will not allow it). Furthermore, the problem is not with the file type (.exe), for the VPN client downloaded fine within a "high" privacy setting in IE. To change this setting go to Tools and then click on "Internet Options." Here's what it looks like:
