A long while back I started a poly series between Alex, Sam, and Lena-- AgentReignCorp, or ARC for short. They become a family unit with Ruby as their daughter, and after a while Ruby brings home her crush/girlfriend, an OC named Bridget.
Bridget is kind of fangirl for Lena Luthor, so she kinda wigs out initially when she realizes Ruby's mom 'Lena' is actually Lena freaking Luthor. Plus she's never really seen a real lesbian relationship (let alone a polyamorous one) which means that ARC become goalz, and their home becomes a safe haven for her, because it's filled with warmth and affection and respect.
Furthermore, Bridget's mom is lowkey homophobic, and while she loves her daughter, she thinks Ruby and her moms are bad influences... until Bridget and her mom's apartment burns down and ARC takes them in temporarily. When they don't expect anything in return, Bridget's mom finally realizes how kind they are and how welcoming they've been of Bridget (Lena especially takes Bridget under her wing), and admits how wrong she'd been to judge them for their... unorthodox relationship.
In a side/partial-canon-to-ARC story, Ruby develops kryptonian abilities, and almost murders one Lena's quarterly assassination attempters in cold blood. But Bridget is there and talks her down, because she knows Ruby better than anyone else (aside from her moms) and knows how to appeal to her better nature, and knows what logic will work on her.
So, tldr; Bridget is an OC for a previous series I did who loved Ruby with all her heart and Ruby loved her back just as hard.