Just grab this http://fus.nanzen.se/download.php?id=12 Under choose a firmware Android > GTi9100 > UK-tmobile & then click check firmware on the left. Then you should get this in the box at the bottom
Hit download & then flash with mobile odin or odin. No need for Kies.
Darryl_1983 Factory reset, wipe everything & then follow the steps above but for the carrier your girlfriend was on.
I downloaded that program and the firmware it recommended, but kies was saying it was not able to upgrade it

I tried another f/w from xda-forums and it isn't even listing it's firmware in kies.....
gahhhh