honestly I see so many jokes about how lena constantly says she can always tell when Kara is lying and that she’s horrible at keeping secrets from her but the thing that’s tragic is that lena is actually pretty damn good at spotting what Kara’s feeling, even when she doesn’t know the actual details. it’s part of what makes them such good friends– they’re emotionally honest with each other.
so even if she doesn’t know that Kara is supergirl she probably knows when Kara is lying. And that’s why she always brings it up, she doesn’t know what it’s about but she knows that it’s happening. And can you imagine little 13 year old lena, watching her beloved big brother slowly descend into madness and she knows something is horribly horribly wrong, but she has no idea what and everyone tells her she’s imagining things, that everything is fine?
she’s never been more upset to discover she’s right.
lena may not know that Kara is supergirl but she does know that Kara is lying to her. except, Kara’s not lex–shes the best person she knows. and she’s not lying to any of her other friends or her sister, so it’s just to lena–she can’t fault Kara for that. she’s trying, but she’s a luthor after all. if the most moral person she’s ever met doesn’t trust her then maybe she shouldn’t be trusted.