What happened was that 6GB PST file was on the client's server and not on their local machine. Once I removed that data file Outlook opened fine, but now I still needed to transfer the e-mails from that PST into smaller ones. So, I copied the 6GB PST to her local machine, added it to the "Data Files" list under Mail in Control Panel and then opened Outlook. Outlook opened and then I dragged and dropped the e-mails to another PST file that I made (New->Outlook Data File) and then Compacted the PST file.
