Spoiler
I will repost what I already said in a previous comment a few month ago after the lastest interlude public release :
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As I pointed out in some youtube video long ago, this was already hinted back in their first encounter (with Lance). Not only the plant caring trait was present, but her kinda crude and teasing way of speaking, her poneytail, and most of all her "tag" in the Resoom / Current organisation, as Artemis addressed her as "N°2", were already pointing out in the fact she might be older and different from the actuals carriers (like, number two of what ? Certainly not carriers since they've been "harvested" for centuries).
The new interlude just cemented the fact out of mere hypothesis once and for all by bringing new hints about her father and Damion. There's now too many hints to even need her to be addressed as Diana anymore to confirm it.
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In others words, if there was still a lot of room for doubt with only their first meeting, 99,99% confirmed now after the second during the interlude.
As for "how", and now this is pure theory, since Dr Liao suicided before the plans for his surgery on Cyrus were brought to Darius, maybe he, not wanting to risk his precious asset that is Cyrus to him, experimented instead on Diana, the other last "link" he could have at hand with Dr Liao (maybe he asked her if he or Cyrus told her about the experiment process and tried to replicate it from whatever intel she had, while telling her Cyrus has passed too somehow to keep her from questionning about him when she was in the facility) to gain access to expanded lifespan for himself afterward. Would explain how the two of them are still alive alongside Cyrus (Vita mentioned the regulars carrier's lifespan isn't extended that significantly compared to a normal person), along with the "N°2" tag (implying 1st to be Cyrus).