I would about die if when it’s revealed that Lena knows about Kara being Supergirl -
Maybe after she’s been roped into helping the DEO for some assistance in highly advanced tech, and Lena gets a comm directly to supergirl having to talk her through disarming a bomb like device. Lena accidentally mutters a “Please make it back okay Kara”. No one else but Kara is able to hear it and by the time she gets back to the DEO, Lena is passed out on a nearby desk from pulling a 48 hour shift like the rest of the crew. Alex meets Kara at the entrance and mentions how much help Lena was able to provide and “maybe you were right about her.”
Kara offers to fly the still passed out Lena home. Once they finally get there Lena manages to wake up and Kara mentions they should probably have a talk.
Settling next to Lena on her bed She asks “How did you know it was me?”
Lena barely able to keep her eyes open replies, “No one else looks at me the way you do”
“And how is that?”
“Like I’m not a monster”