>>715864562
based on the lore its the explanation that makes the most sense.
there are very few people she would care about in terms of "how do I look to them" and the master chief rather quickly moved his way up to the top of the list.
That said, I would not consider her look in halo 2 to reflect that relationship.
It is more likely to reflect the aftermath of "digesting" everything she got out of the Forerunner networks greatly expanding her "size" as a smart AI.
She became far more complex as a result of that, and chose a much more detailed form as a result.
In halo 3 she was still in that form because she had no reason to change it.
Halo 4 was the deliberate "I want you to want me" look after chief rescued her in halo 3 from the utter hell of the gravemind slowly looking to corrupt her and they embraced death together at the end of the game.
Same unspoken language as padme dressing up in the "take me now" dress while telling anakin they cannot be together.
