Most logical place is after story of main game has ended.
Tagged as has spoilers about ending of HZD.
Aloy has ended her personal quest of learning about herself and who she is, even got to visit her real... home and meet herself. So to speak. Also just because Sylens has Hades or what remains of it doesn't mean they come up with some nutty world domination plans instantly so Aloy has time to explore world and stumble upon new mysteries. Like here.
She never considered Elizabet to be
herself, or even wrestled with that idea, which is a fairly significant failing of the writing. So her visiting the source of her DNA is sad for the audience because we connected with that character (maybe more than Aloy, another failing of the writing), but its meaningless to her insofar as how Aloys character was written. The beauty in the reveal of the mechanical flowers, all of that is totally lost on Aloy, because she never acknowledges i