It is quite straightforward. I came through in fall of 2005 with my now husband and stepson. It looked like it hasn't changed for about 50 years, so I doubt it's changed in the last two...
USC's go to the right in the Customs Hall, your fiancee will go to the left. If she's not sure, there will be a CPB officer around there to ask.
She will go to a little booth where a CPB officer sits. She gives him/her The Sealed Envelope (from the Consulate) containing all her paperwork and her passport. The officer will open the envelope and go through the papers and enter a few things in the computer. He/she will then probably ask her to do some minor biometrics (fingerprint, photo, maybe retinal scan.... I can't remember exactly). Then the officer will tell her to go to a smaller room off to the left. This place really looks like time forgot it... very 50's post modern bureaucrat style... dingy and unattractive. Lots of chairs there to collapse in while they finish the paperwork. There's a big, elevated counter at the front where another officer will look over her papers and put the I-94 in her passport and probably stamp the back of it with the temporary EAD. I checked my husband's passport for the temp EAD before leaving this room.
Then she walks through the doors to the inspection area (with those routine questions from the Ag inspectors about what she's bringing into the country... ). And THEN she walks through another set of doors where YOU are waiting for her and you all start your new life together!!
Best wishes....
Maya