Supergirl, Season 4

Kara:
I had no idea your brother's history with Mercy went back this far.

Lena:
Yeah. Mercy started out as his head of security, but over time she became his closest confidant and frequent dinner guest.

Kara:
I knew Lex had a close relationship with her, but I-I had no idea you did.

Lena:
Growing up, my mother was very critical of me, as you know. She wasn't very helpful with the life stuff. Then Mercy came into our lives and she kind of took me under her wing. She taught me how to act, how to dress, how to always reach for the biggest gun. She was almost like a big sister. Almost.

Kara:
Was it hard for you after she left Lex?

Lena:
Yeah. I felt abandoned. But I really can't blame her. Truthfully, I blame Lex entirely.

Kara:
What happened between them?

Lena:
Mercy grew frustrated because Lex was so hyper-focused on Superman. He lost sight of the bigger picture. She felt intelligence wasn't enough, that humans needed to develop even greater powers and abilities than aliens.

Kara:
That sounds unhinged.

Lena:
Yeah. But I don't disagree with her main point. [seeing Kara's look of surprise] Well, why can't humans be as powerful as aliens?