Warning: spoilers ahead for Episode 2 of Supergirl Season 3, called "Trigger."
Ever since Lena Luthor made her Supergirl debut back in the beginning of Season 2, fans have been wondering if Lena would go the way of the villainous Lex and turn on Kara. Lena so far has been a good friend to Kara and a valuable ally in National City, and she's firmly on the side of the good guys of the show. That said, she is still a Luthor, and she's open about how well she's been trained in deception. The events of "Trigger" revealed that Lena is arguably the most dangerous person on Supergirl.
In "Trigger," Lena took her place at CatCo after buying the company back in the Season 3 premiere. James and Kara had assumed that Lena would be a hands-off exec who stayed at L-Corp for her day job, but Lena quickly proved in the episode that she plans on keeping a close watch on her new investment. After spending hundreds of millions of dollars on it, she understandably wants to be kept in the loop on the goings-on of the media conglomerate.
Lena made it clear to both Kara and James that she's not above pulling rank at CatCo if the situation calls for it. She may be on the side of the good guys, but she's also a shrewd businesswoman who owns a large news outlet. If she decides to start controlling the press coming out of CatCo, she could quickly become an enemy. She's rich, powerful, and not accustomed to working with friends rather than minions. With Kara lying to her about some major aspects of her life, Lena could conceivably turn on her friend.
Ownership of CatCo and her millions of dollars isn't the only way Lena became more dangerous in "Trigger." We learned the identity of the person who will run the business at L-Corp in Lena's absence, and that person is none other than Samantha Arias, a.k.a. the new villain Reign. Admittedly, the woman herself doesn't know that she has superpowers at the moment, and she hasn't undergone the transformation that will presumably take her from single mom Sam to supervillain Reign. Still, she has already shown that she's grateful to Lena for the opportunity and--more importantly--the money. Lena could have a superpowered ally firmly in her corner if she does turn on Kara.
"Trigger" didn't transform Lena into a fighter who could hold her own against even the non-powered human badasses, but she has more resources than ever that could make her a formidable foe for Kara, the D.E.O., and the CatCo crew if she turns. While obviously viewers are going to be rooting for Kara and Team Supergirl, we probably won't be able to blame Lena if she lashes out after discovering the gigantic secret and the mountain of lies that have been served her way courtesy of her best pal.
Hopefully Lena won't lash out by channeling her evil brother's intentions, and she could remain firmly on the side of the good guys for the entire run of the series. We should just probably keep an eye on her while she has so much power in so many different arenas. All things considered, I'd say that we're in for an exciting third season of Supergirl.
New episodes of Supergirl air on Mondays at 8 p.m. ET on The CW.