She tests the alien device on herself, before showing it to Kara.
(Lena’s always wondered, privately, who her mother was. What kind of person would fall for her father, and leave her behind- even if she had died when Lena was 4, she always could’ve made other arrangements. She could’ve lived an entirely different life, without ever knowing she was a Luthor. But that hadn’t happened, and now here she was, twenty years later with a new invention in her hand.)
She thinks it failed, at first.
There’s no way it could’ve turned red, instead of green.
Red meant alien, meant not to be trusted, if you were from her family. Meant the color of a certain cape, that tormented Lena’s vision whenever she closed her eyes and thought about her brother. Meant the color of yet another, in her new city, attached to the shoulders of a woman who- so far- had only saved her life, and meant her no harm.
She was starting to like that color.
But she didn’t know what it meant for her, especially when her mother found out.
Because she would.
In the meantime, however, Lena would just have to repair the device, and make sure, the next time she showed it off to someone, it would turn green for her.
It had to.