tbh i dont really like high school aus all that much, and Lena would never be in public school while living with the Luthors so
1) They’re all in boarding school together. Eliza thought it might be good for Alex to get a change of scenery after the first year that Jeremiah died, and she was kinda feeling overwhelmed as a single parent, especially to two geniuses.
2) The school was willing to work with Kara both her SPD (sensory processing disorder, because that’s essentially what Kara has) and her off the chart math and science abilities but extremely subpar English and history. in fact
3) The only one there that can keep up with Kara is one Lena Luthor–they share a private tutor for this one. Lena has always been the best at science and math, before only Lex able to come close to touching her, she’s won every award she could for her age, received every accolade and here’s this new girl out of the fucking blue blowing everything she’s done out of the water, doing math problems that take her months to complete and parse out in just seconds
lena tries being jealous and mad but kara makes it so hard to do that she’s just so nice and friendly and doesnt treat her like she’s THE lex luthor’s baby sister (because yeah, right now lex is the golden boy who’s supposed to save the world), or that her family is richer than god–she just treats her like a friend and god she’s so pretty (but yes, imagine a little bit paris geller “get out of my school” for a bit, but a lot kara doesnt even pick up on kara is not oblivious but she was not socialized on earth, and also is dealing with a bunch of trauma and constant sensory overload ok)
3) also a lot of things lena thinks she’s doing something mean and paris geller like that to her seem like she’s sending a message to kara but by kryptonian standards that message is not “i’m top dog” but “this is my way of wooing you and proving that I would be a good match.” Poor kara is very confused when alex is like oh im so sorry you have to spend all this time with lena when she hates you and kara is like ??????? she wrote a thing in a scientific journal for me what do you MEAN she hates me
4) maggie is there on scholarship she worked her ass off and is very little and the world is hurting her and she’s like you know what maybe i’m not gay maybe i just dont like anyone. and then sees alex running towards her with her surfboard and in a bikini and is like n e v er mIND
5) alex and kara are roommates bc siblings and they wanna keep them together but maggie and lena are also roommates and they both agree the danvers sisters should come with a warning