So, along the lines of time traveling Kara, I give you Big Sister Kara. Due to things being waaaay too skewed for this lil headcanon if she shows up on time, we’re gonna keep running with the Phantom Zone stuckage and just have Kara arrive a little earlier. Say, around the time Alex is ten years old.Now since Alex isn’t responsible for Kara, how does their dynamic change? What does it mean to have Kara as the protective one?
Kara crash lands as she does and gets picked up by her super cousin and dropped off with the Danvers. Except instead of a teenage Alex, there’s a ten year old Alex asking Clark all kinds of questions from Jeremiah’s side. And Kara probably don’t speaketh the English, so I’m headcanoning that Clark gave the Danvers some kind of translation device. Which of course lil Alex snags and drags Kara away to introduce her to the other member of the family, Schrodinger the cat (yes I will run with this Stargate joke until the end of time)
There is a part of Alex that resents Kara for interrupting her only-child lifestyle. For the most part, though, she likes her new big sister. And for all her faults, Eliza wouldn’t hold a 10-year-old’s academics and behavior against a 14-year-old from an advanced planet. Alex would still be allowed to be a kid, Kara went into the Phantom Zone ready to take care of someone, and so they usually get along.