Ok, so another update. I ordered a Virgin Mobile Canada Micro SIM from ebay, and followed all the steps for both access points on the SIM (a Bell and a Virgin AP), the Bell one didn't work in my wife's 1020, but the Virgin AP changed the message that I received on the phone. I double checked and triple checked the AP settings for T-Mobile, and everything was as it should be. I reinstalled Access Point, with the T-Mobile SIM in, and tried the internet sharing and it worked just fine. Connected a laptop to it and all. When I rebooted the phone, a message then pops up saying Internet tethering is not authorized on this account (or something like that). Now her internet sharing and MMS won't work, when MMS has been fine this whole time.
I'm trying the process on my 1520 right now and will update with those results...