Dammit, that's who I was gonna bet on too, y'all. It doesn't work if we all back the same person, lol.
If, as you say, she will work in Cat Co, how about Kara herself? ;-) But, that would be non-canon. (Nope! I don't back it; James seems like possible to me though I never considered a canon romance till I read this thread; or Winn if they are kicking Lyra out.) But, I do find the thought amusing.

t:
Canon would be, if they develop a friendship with Kara as well, they would use that to contrast Kara-Lena because they were so invested in it last year (I mean, this year, as in S2).
Which could again cause shipping wars (Supercorp vs. Superreign, Sanvers vs. Alex-Reign--which is also a possibility if they share screen time at all; there was a lot of Alex-Astra in S1). Ha! Twitter is best to be kept out of.
Whatever happens, I'd really like to see Kara struggle with her family's and her planet's legacy. There was potential there in S2, which was not realised; or may be was pushed to S3?
Also, do worldkillers have redeeming potential? Because if it is all black and white, it may lose some of the tension (for me). I like it when there is a will-they won't they with villains but, which is actually exploited in the story not just in acting. Like Astra and unlike Non.