I imagine it like this: At first we hear a phone ringtone, and then we see Elizabet Sobeck lying on her bed. Later she leaves her house (she is probably going to work in the Faro Automated Solutions) and while she is walking on the sidewalk to a bus station, the camera turns up and we see Aloy climbing on the lamposts, trying to follow Sobeck.
And while the player thinks I am crazy (because the following theory is a very mind-blowing one), there goes a small flashback:
Aloy and her squad are back at cauldron GEMINI, this time to trap HEAPHESTUS for the second time (without anyone to die, hopefully). When Aloy and Beta are ready to override the cauldron's cores a hord of machines appear, and one of them carries a huge thing full of wires and machine parts. Before someone realises, the machines activate the weird thing and send Aloy and her companies to the PAST!!!!!!!
Now the characters are scattered across the Old Ones' world, and have to find a way to return to the present.
Aloy feels lost and doesn't know what to do, so she wants to find Elisabet.
She arrives to the FAS headquarters and Aloy finds a way to enter the building. When she is ready to talk to Elisabet, Sylens contacts Aloy from his focus and says:
"Aloy, HEAPHESTUS sent us to the past because they knew you were going to find Elisabet, and if you talk to her she might never make GAIA, and that means you, me and the whole world we know would have never existed! Are you sure you want to do this? Then your mission of saving the humanity would fail- do you really want that?"
Since Aloy cannot interact with Elisabet she must find a way to return to the present.
That's what I think for the first mission, and I think it'd be a shame to not return to a new map and stay trapped to the past, in the second mission I find it better for her to return back to the world we know.
What do you think?