I'm holding a Photon in my hand right now with Google Talk open and there's no option for "video chat" anywhere.
I'll also note that not 1 of the reviews of the phone has mentioned it having Google Talk video support. And MobileTechReview, in their video review, went as far as to dispel the rumor that it does. Also, if you read to the end of the 1st link, the Motorola forum manager had this to say on the matter:
"We expect this to be enabled in a future update. There is no hard date at this time of then it will be available.
Mark
Support Forums Manager"
Here's the link once again
https://supportforums.motorola.com/message/438413
Motorola even says on their Photon support page that Google Talk video chat isn't supported
https://motorola-enterprise.custhelp.com/app/answers/detail/a_id/69149/~/photon-4g---video-chat
There's some work being done over on XDA to right this wrong
Google Talk Video not supported - xda-developers
Since your girlfriends phone is able to access Google Talk video chat, I'm sure all the Photon owners would be eternally grateful if you would be so kind as to post pics or video and instructions on how to access it.