When Lena Luthor (Katie McGrath) showed up in National City last season, the friendship she struck up with Kara (Melissa Benoist) immediately resonated with fans.

“What I forget often is that people watch what we do,” McGrath tells Variety. “I know that sounds strange, but we’re focused on making it as real as possible, and it’s not until it gets out there that people are affected by it. It’s quite touching to know that something that you’ve done has had such an affect and impact on people. Neither myself or Melissa had any idea – until it came out – how much it affected people.”

That friendship may have hit a rough patch when Lena started working with her mother to unknowingly help make the planet poisonous to Daxamites, ultimately forcing Mon-El (Chris Wood) to leave the planet in the second season. And now, Lena will be dealing with the guilt of some of her choices.

Variety spoke with McGrath about how that guilt will manifest itself in Season 3, including where and Kara stand in Season 3 and what CatCo will look like with her in charge.

In the third season premiere, it seemed like Kara may still be harboring a bit of resentment toward Lena for her actions at the end of Season 2. How does their relationship evolve this season?

Lena feels very guilty. She feels partially responsible for what happened to Mon-El. Kara being her best friend, it kills Lena to see her unhappy – and the fact that she might have inadvertently caused that is hugely disturbing and damaging to her. The friendship she has with Kara is her most important relationship in the show, and she wouldn’t want to jeopardize that or harm that. The thought that she may have done that is hard for her to bear.

When she first showed up, Lena said she was trying to change the stigma of her last name. After what happened last season does she think that is still possible, or does the Luthor name just sow chaos?

Well, chaos does tend to follow Lena wherever she goes. I think it’s very difficult for her because she’s attempting to do the right thing and everything she does comes from that place. When you try to do something with good intentions and hear it’s been taken somewhere so negatively it’s always difficult. I don’t think she expects that every time. She thinks “I’ve actually done the right thing and I’m the victim here,” yet she’s still vilified for having the last name. It’s tough for her, but she doesn’t give up. Lena’s not a quitter.

Was her guilt the motivation behind buying CatCo?

It’s funny because when I read it I thought, “Lena, this seems like a long way to go for your best friend.” But at the same time, she’s a young woman who is in charge of essentially the biggest organization in the world and she’s not going to make a business decision based purely on emotion. While it is possibly motivated by her guilt, it’s also a way to stand up and combat Morgan Edge [Adrian Pasdar], and it’s also viewed as a challenge. It’s not something she knows a lot about, and it’s easy for her to become complacent to do a job she could do standing on her head, but this is a different challenge for her.

Does she struggle with running a multimedia empire on top of all her other responsibilities?

One of the great things about Lena is that she doesn’t pretend that she knows everything or that she has all the answers. She’s very open about the fact that there are things she doesn’t know or understand, but she’s going to run it the way she thinks with her intelligence – but part of being a good manager is knowing when to ask for help and hire the best people. She has that in James [Mehcad Brooks] and Kara.

How does James react to the news that Lena bought CatCo?

I think he’s surprised. Initially, he’s thankful that it’s been bought by someone who is not Morgan Edge, but he’s surprised that Lena wants to be so hands-on. There’s some friction and tension because this is his realm, his kingdom, and I don’t want to say there is a conquering empress coming in but yeah.

Swooping in and buying CatCo out from under Morgan Edge was a serious power move. How does that affect their already strained relationship?

I don’t think Morgan Edge is a man who takes kindly to being upstaged by a woman.

New episodes of “Supergirl” are on Mondays at 8 p.m. on the CW.