What does my GF need to bring to the Amphor (or can she use post office?) to apply for a passport? I've done a google search of the internet and a search here but can't really find any clear cut answer. TIA

She cannot get a passport at the Amphur.

She will need to go to an office of The Ministry of Foriegn Affairs.

As for ID, here is the link to MFA Thailand with the details

The locations of their offices are also on this website.

Main office is:

Chaengwattana Building

Address :123 Chaengwattana Rd., Tungsonghong Laksi Bangkok 10210. Tel. (662) 981-7171

If you google Thai passport, it will also give you the information

More locations:

Office of Passport Division