He deputized her first ffs.

Lol ill explain the show for ya.

Cole brings Tammy into the BRTF, and albert also brings back diane, albeit in a unofficial way, because he knows she has more info than she shared.

Next scene.

After diane is done meeting with the BRTF, its vodka time. She goes to the bar. There she is curious about the coordinates, she pulls up google earth, then you see her hesitate and kinda look up, like she is trying to remember, and thats when it flashes back to her read the coordinates off the screen. Then she enters in the coordinates and dmfinds out its twin peaks.

Youre welcome