Is it possible that the woman who betrayed Horizon in the STFO trailer is Ash before she was a simulacrum? Yes, and we'll look at the sources which point to this.
Logic
First, I want to address something. The incident where the woman betrayed Horizon was 87 years ago, however Ash is a simulacrum, meaning she can live until her source is destroyed, so it's possible that the woman was Ash as a human being.
The only bit of logic which may hold this theory back is the fact that it's also possible Ash is not from the Outlands, and is actually from the planet Typhon. We know that simulacrum Ash worked for the IMC, who were situated away from the Outlands in another part of the Frontier (about 20 years away).
The Broken Ghost
In the final quest, we hear Ash spilling out random information from her memory, including:
"Do you fear me, pilot?" - most likely a reference to her battle against Jack Cooper in the TF2 campaign.
"Just a wee bit of betrayal before breakfast, eh dearie?" - most likely a reference to Horizon, due to the Scottish dialect and the reference to betrayal
"All roads lead to Branthium" - referring to the Branthium crystals which Horizon and her assistant were required to obtain from the black hole
You can see a lot of references to Horizon in her quotes, meaning they have some sort of connection.
The First Ship
In one of the comics part of the Season 6 quest, Kuben Blisk pays a visit to Ash and tells her "her friend is back". This could refer to anybody, but if human Ash was Horizon's assistant, this would all add up with the S5 quest evidence.
Promise
We know that the reason Horizon's assistant betrayed her is because somebody who had an interest in the Branthium crystals ordered her to. Who do we know has an interest in energy and technology, and have been making lots of deals in the Apex lore? That's right, Hammond! Hammond was a subsidiary of the IMC during the events of Titanfall, and Ash as both a human and simulacrum worked for the IMC. It all adds up!
