While going through the ‘b’ route.
On Chapter 11, Choose A,B,C,A,C, in order.
Keep progressing through the story until it pops.
Reaver Lion said after choosing to the options to:
Head out the office and go all the way down to the archives at the end of the hallway and find Amara’s belongings.
They are on the right side on a shelf as you enter the archives. Pick them up and head over to the table in the left corner then open it. Read her journal, then follow the music box sound to the 1st door on the right,then the third locker on the left..
Pick the music box up and head down stairs past the lift to the now open doorway to the garden.Walk to the far right go through the hole in fence turn left and go up the hill then keep going till you see a rusty car by a lamppost,
just in front to the left is a gate open it..go through watch a cutscence then..pop :)